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{{task}}Syntax Analyzer
A Syntax analyzer transforms a token stream (from the [[Compiler/lexical_analyzer|Lexical analyzer]]) into a Syntax tree, based on a grammar.
{{task heading}}
Take the output from the Lexical analyzer [[Compiler/lexical_analyzer|task]], and convert it to an [https://en.wikipedia.org/wiki/Abstract_syntax_tree Abstract Syntax Tree (AST)], based on the grammar below. The output should be in a [[Flatten_a_list|flattened format.]]
The program should read input from a file and/or stdin, and write output to a file and/or stdout. If the language being used has a parser module/library/class, it would be great if two versions of the solution are provided: One without the parser module, and one with.
{{task heading|Grammar}}
The simple programming language to be analyzed is more or less a (very tiny) subset of [[C]]. The formal grammar in [https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_Form Extended Backus-Naur Form (EBNF)]:
stmt_list = {stmt} ;
stmt = ';'
| Identifier '=' expr ';'
| 'while' paren_expr stmt
| 'if' paren_expr stmt ['else' stmt]
| 'print' '(' prt_list ')' ';'
| 'putc' paren_expr ';'
| '{' stmt_list '}'
;
paren_expr = '(' expr ')' ;
prt_list = (string | expr) {',' (String | expr)} ;
expr = and_expr {'||' and_expr} ;
and_expr = equality_expr {'&&' equality_expr} ;
equality_expr = relational_expr [('==' | '!=') relational_expr] ;
relational_expr = addition_expr [('<' | '<=' | '>' | '>=') addition_expr] ;
addition_expr = multiplication_expr {('+' | '-') multiplication_expr} ;
multiplication_expr = primary {('*' | '/' | '%') primary } ;
primary = Identifier
| Integer
| '(' expr ')'
| ('+' | '-' | '!') primary
;
The resulting AST should be formulated as a Binary Tree.
;Example - given the simple program (below), stored in a file called while.t, create the list of tokens, using one of the Lexical analyzer [[Compiler/lexical_analyzer|solutions]]
lex < while.t > while.lex
;Run one of the Syntax analyzer [[Compiler/syntax_analyzer|solutions]]:
parse < while.lex > while.ast
;The following table shows the input to lex, lex output, and the AST produced by the parser:
{| class="wikitable" |- ! Input to lex ! Output from lex, input to parse ! Output from parse |- | style="vertical-align:top" |
count = 1;
while (count < 10) {
print("count is: ", count, "\n");
count = count + 1;
}
| style="vertical-align:top" |
1 1 Identifier count
1 7 Op_assign
1 9 Integer 1
1 10 Semicolon
2 1 Keyword_while
2 7 LeftParen
2 8 Identifier count
2 14 Op_less
2 16 Integer 10
2 18 RightParen
2 20 LeftBrace
3 5 Keyword_print
3 10 LeftParen
3 11 String "count is: "
3 23 Comma
3 25 Identifier count
3 30 Comma
3 32 String "\n"
3 36 RightParen
3 37 Semicolon
4 5 Identifier count
4 11 Op_assign
4 13 Identifier count
4 19 Op_add
4 21 Integer 1
4 22 Semicolon
5 1 RightBrace
6 1 End_of_input
| style="vertical-align:top" |
Sequence
Sequence
;
Assign
Identifier count
Integer 1
While
Less
Identifier count
Integer 10
Sequence
Sequence
;
Sequence
Sequence
Sequence
;
Prts
String "count is: "
;
Prti
Identifier count
;
Prts
String "\n"
;
Assign
Identifier count
Add
Identifier count
Integer 1
;Specifications
;List of node type names:
Identifier String Integer Sequence If Prtc Prts Prti While Assign Negate Not Multiply Divide Mod
Add Subtract Less LessEqual Greater GreaterEqual Equal NotEqual And Or
In the text below, Null/Empty nodes are represented by ";".
;Non-terminal (internal) nodes:
For Operators, the following nodes should be created:
Multiply Divide Mod Add Subtract Less LessEqual Greater GreaterEqual Equal NotEqual And Or
For each of the above nodes, the left and right sub-nodes are the operands of the respective operation.
In pseudo S-Expression format:
(Operator expression expression)
Negate, Not
For these node types, the left node is the operand, and the right node is null.
(Operator expression ;)
Sequence - sub-nodes are either statements or Sequences.
If - left node is the expression, the right node is If node, with it's left node being the if-true statement part, and the right node being the if-false (else) statement part.
(If expression (If statement else-statement))
If there is not an else, the tree becomes:
(If expression (If statement ;))
Prtc
(Prtc (expression) ;)
Prts
(Prts (String "the string") ;)
Prti
(Prti (Integer 12345) ;)
While - left node is the expression, the right node is the statement.
(While expression statement)
Assign - left node is the left-hand side of the assignment, the right node is the right-hand side of the assignment.
(Assign Identifier expression)
Terminal (leaf) nodes:
Identifier: (Identifier ident_name) Integer: (Integer 12345) String: (String "Hello World!") ";": Empty node
;Some simple examples Sequences denote a list node; they are used to represent a list. semicolon's represent a null node, e.g., the end of this path.
This simple program:
a=11;
Produces the following AST, encoded as a binary tree:
Under each non-leaf node are two '|' lines. The first represents the left sub-node, the second represents the right sub-node:
(1) Sequence
(2) |-- ;
(3) |-- Assign
(4) |-- Identifier: a
(5) |-- Integer: 11
In flattened form:
(1) Sequence
(2) ;
(3) Assign
(4) Identifier a
(5) Integer 11
This program:
a=11;
b=22;
c=33;
Produces the following AST:
( 1) Sequence
( 2) |-- Sequence
( 3) | |-- Sequence
( 4) | | |-- ;
( 5) | | |-- Assign
( 6) | | |-- Identifier: a
( 7) | | |-- Integer: 11
( 8) | |-- Assign
( 9) | |-- Identifier: b
(10) | |-- Integer: 22
(11) |-- Assign
(12) |-- Identifier: c
(13) |-- Integer: 33
In flattened form:
( 1) Sequence
( 2) Sequence
( 3) Sequence
( 4) ;
( 5) Assign
( 6) Identifier a
( 7) Integer 11
( 8) Assign
( 9) Identifier b
(10) Integer 22
(11) Assign
(12) Identifier c
(13) Integer 33
;Pseudo-code for the parser.
Uses [https://www.engr.mun.ca/~theo/Misc/exp_parsing.htm Precedence Climbing] for expression parsing, and [https://en.wikipedia.org/wiki/Recursive_descent_parser Recursive Descent] for statement parsing. The AST is also built:
def expr(p)
if tok is "("
x = paren_expr()
elif tok in ["-", "+", "!"]
gettok()
y = expr(precedence of operator)
if operator was "+"
x = y
else
x = make_node(operator, y)
elif tok is an Identifier
x = make_leaf(Identifier, variable name)
gettok()
elif tok is an Integer constant
x = make_leaf(Integer, integer value)
gettok()
else
error()
while tok is a binary operator and precedence of tok >= p
save_tok = tok
gettok()
q = precedence of save_tok
if save_tok is not right associative
q += 1
x = make_node(Operator save_tok represents, x, expr(q))
return x
def paren_expr()
expect("(")
x = expr(0)
expect(")")
return x
def stmt()
t = NULL
if accept("if")
e = paren_expr()
s = stmt()
t = make_node(If, e, make_node(If, s, accept("else") ? stmt() : NULL))
elif accept("putc")
t = make_node(Prtc, paren_expr())
expect(";")
elif accept("print")
expect("(")
repeat
if tok is a string
e = make_node(Prts, make_leaf(String, the string))
gettok()
else
e = make_node(Prti, expr(0))
t = make_node(Sequence, t, e)
until not accept(",")
expect(")")
expect(";")
elif tok is ";"
gettok()
elif tok is an Identifier
v = make_leaf(Identifier, variable name)
gettok()
expect("=")
t = make_node(Assign, v, expr(0))
expect(";")
elif accept("while")
e = paren_expr()
t = make_node(While, e, stmt()
elif accept("{")
while tok not equal "}" and tok not equal end-of-file
t = make_node(Sequence, t, stmt())
expect("}")
elif tok is end-of-file
pass
else
error()
return t
def parse()
t = NULL
gettok()
repeat
t = make_node(Sequence, t, stmt())
until tok is end-of-file
return t
;Once the AST is built, it should be output in a [[Flatten_a_list|flattened format.]] This can be as simple as the following:
def prt_ast(t)
if t == NULL
print(";\n")
else
print(t.node_type)
if t.node_type in [Identifier, Integer, String] # leaf node
print the value of the Ident, Integer or String, "\n"
else
print("\n")
prt_ast(t.left)
prt_ast(t.right)
;If the AST is correctly built, loading it into a subsequent program should be as simple as:
def load_ast()
line = readline()
# Each line has at least one token
line_list = tokenize the line, respecting double quotes
text = line_list[0] # first token is always the node type
if text == ";" # a terminal node
return NULL
node_type = text # could convert to internal form if desired
# A line with two tokens is a leaf node
# Leaf nodes are: Identifier, Integer, String
# The 2nd token is the value
if len(line_list) > 1
return make_leaf(node_type, line_list[1])
left = load_ast()
right = load_ast()
return make_node(node_type, left, right)
Finally, the AST can also be tested by running it against one of the AST Interpreter [[Compiler/AST_interpreter|solutions]].
;Test program, assuming this is in a file called prime.t: lex <prime.t | parse
{| class="wikitable" |- ! Input to lex ! Output from lex, input to parse ! Output from parse |- | style="vertical-align:top" |
/*
Simple prime number generator
*/
count = 1;
n = 1;
limit = 100;
while (n < limit) {
k=3;
p=1;
n=n+2;
while ((k*k<=n) && (p)) {
p=n/k*k!=n;
k=k+2;
}
if (p) {
print(n, " is prime\n");
count = count + 1;
}
}
print("Total primes found: ", count, "\n");
| style="vertical-align:top" |
4 1 Identifier count
4 7 Op_assign
4 9 Integer 1
4 10 Semicolon
5 1 Identifier n
5 3 Op_assign
5 5 Integer 1
5 6 Semicolon
6 1 Identifier limit
6 7 Op_assign
6 9 Integer 100
6 12 Semicolon
7 1 Keyword_while
7 7 LeftParen
7 8 Identifier n
7 10 Op_less
7 12 Identifier limit
7 17 RightParen
7 19 LeftBrace
8 5 Identifier k
8 6 Op_assign
8 7 Integer 3
8 8 Semicolon
9 5 Identifier p
9 6 Op_assign
9 7 Integer 1
9 8 Semicolon
10 5 Identifier n
10 6 Op_assign
10 7 Identifier n
10 8 Op_add
10 9 Integer 2
10 10 Semicolon
11 5 Keyword_while
11 11 LeftParen
11 12 LeftParen
11 13 Identifier k
11 14 Op_multiply
11 15 Identifier k
11 16 Op_lessequal
11 18 Identifier n
11 19 RightParen
11 21 Op_and
11 24 LeftParen
11 25 Identifier p
11 26 RightParen
11 27 RightParen
11 29 LeftBrace
12 9 Identifier p
12 10 Op_assign
12 11 Identifier n
12 12 Op_divide
12 13 Identifier k
12 14 Op_multiply
12 15 Identifier k
12 16 Op_notequal
12 18 Identifier n
12 19 Semicolon
13 9 Identifier k
13 10 Op_assign
13 11 Identifier k
13 12 Op_add
13 13 Integer 2
13 14 Semicolon
14 5 RightBrace
15 5 Keyword_if
15 8 LeftParen
15 9 Identifier p
15 10 RightParen
15 12 LeftBrace
16 9 Keyword_print
16 14 LeftParen
16 15 Identifier n
16 16 Comma
16 18 String " is prime\n"
16 31 RightParen
16 32 Semicolon
17 9 Identifier count
17 15 Op_assign
17 17 Identifier count
17 23 Op_add
17 25 Integer 1
17 26 Semicolon
18 5 RightBrace
19 1 RightBrace
20 1 Keyword_print
20 6 LeftParen
20 7 String "Total primes found: "
20 29 Comma
20 31 Identifier count
20 36 Comma
20 38 String "\n"
20 42 RightParen
20 43 Semicolon
21 1 End_of_input
| style="vertical-align:top" |
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier count
Integer 1
Assign
Identifier n
Integer 1
Assign
Identifier limit
Integer 100
While
Less
Identifier n
Identifier limit
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier k
Integer 3
Assign
Identifier p
Integer 1
Assign
Identifier n
Add
Identifier n
Integer 2
While
And
LessEqual
Multiply
Identifier k
Identifier k
Identifier n
Identifier p
Sequence
Sequence
;
Assign
Identifier p
NotEqual
Multiply
Divide
Identifier n
Identifier k
Identifier k
Identifier n
Assign
Identifier k
Add
Identifier k
Integer 2
If
Identifier p
If
Sequence
Sequence
;
Sequence
Sequence
;
Prti
Identifier n
;
Prts
String " is prime\n"
;
Assign
Identifier count
Add
Identifier count
Integer 1
;
Sequence
Sequence
Sequence
;
Prts
String "Total primes found: "
;
Prti
Identifier count
;
Prts
String "\n"
;
; Additional examples
Your solution should pass all the test cases above and the additional tests found '''[[Compiler/Sample_programs|Here]]'''.
{{task heading|Reference}}
The C and Python versions can be considered reference implementations.
;Related Tasks
- [[Compiler/lexical_analyzer|Lexical Analyzer task]]
- [[Compiler/code_generator|Code Generator task]]
- [[Compiler/virtual_machine_interpreter|Virtual Machine Interpreter task]]
- [[Compiler/AST_interpreter|AST Interpreter task]]
__TOC__
ALGOL W
begin % syntax analyser %
% parse tree nodes %
record node( integer type
; reference(node) left, right
; integer iValue % nString/nIndentifier number or nInteger value %
);
integer nIdentifier, nString, nInteger, nSequence, nIf, nPrtc, nPrts
, nPrti, nWhile, nAssign, nNegate, nNot, nMultiply
, nDivide, nMod, nAdd, nSubtract, nLess, nLessEqual
, nGreater, nGreaterEqual, nEqual, nNotEqual, nAnd, nOr
;
string(14) array ndName ( 1 :: 25 );
% tokens - names must match those output by the lexical analyser %
integer tkType, tkLine, tkColumn, tkLength, tkIntegerValue;
integer tOp_multiply , tOp_divide , tOp_mod , tOp_add
, tOp_subtract , tOp_negate , tOp_less , tOp_lessequal
, tOp_greater , tOp_greaterequal , tOp_equal , tOp_notequal
, tOp_not , tOp_assign , tOp_and , tOp_or
, tLeftParen , tRightParen , tLeftBrace , tRightBrace
, tSemicolon , tComma , tKeyword_if , tKeyword_else
, tKeyword_while , tKeyword_print , tKeyword_putc , tIdentifier
, tInteger , tString , tEnd_of_input
, MAX_TOKEN_TYPE, PRIMARY_PREC
;
string(16) array tkName ( 1 :: 31 );
integer array tkPrec, tkNode ( 1 :: 31 );
% string literals and identifiers - uses a linked list - a hash table might be better... %
string(1) array text ( 0 :: 4095 );
integer textNext, TEXT_MAX;
record textElement ( integer start, length; reference(textElement) next );
reference(textElement) idList, stList;
% returns a new node with left and right branches %
reference(node) procedure opNode ( integer value opType; reference(node) value opLeft, opRight ) ; begin
node( opType, opLeft, opRight, 0 )
end opNode ;
% returns a new operand node %
reference(node) procedure operandNode ( integer value opType, opValue ) ; begin
node( opType, null, null, opValue )
end operandNode ;
% reports an error %
procedure synError( integer value line, column; string(80) value message ); begin
integer errorPos;
write( i_w := 1, s_w := 0, "**** Error at(", line, ",", column, "): " );
errorPos := 0;
while errorPos < 80 and message( errorPos // 1 ) not = "." do begin
writeon( s_w := 0, message( errorPos // 1 ) );
errorPos := errorPos + 1
end while_not_at_end_of_message ;
writeon( s_w := 0, "." )
end synError ;
% reports an error and stops %
procedure fatalError( integer value line, column; string(80) value message ); begin
synError( line, column, message );
assert( false )
end fatalError ;
% prints a node and its sub-nodes %
procedure writeNode( reference(node) value n ) ; begin
% prints an identifier or string from text %
procedure writeOnText( reference(textElement) value txHead; integer value txNumber ) ;
begin
reference(textElement) txPos;
integer count;
txPos := txHead;
count := 1;
while count < txNumber and txPos not = null do begin
txPos := next(txPos);
count := count + 1
end while_text_element_not_found ;
if txPos = null then fatalError( 0, txNumber, "INTERNAL ERROR: text not found." )
else for cPos := 0 until length(txPos) - 1 do writeon( text( start(txPos) + cPos ) );
if text( start(txPos) ) = """" then writeon( """" );
end writeOnText ;
if n = null then write( ";" )
else begin
write( ndName( type(n) ) );
if type(n) = nInteger then writeon( iValue(n) )
else if type(n) = nIdentifier then writeOnText( idList, iValue(n) )
else if type(n) = nString then writeOnText( stList, iValue(n) )
else begin
writeNode( left(n) );
writeNode( right(n) )
end
end
end writeNode ;
% reads a token from standard input %
procedure readToken ; begin
% parses a string from line and stores it in a string in the text array %
% - if it is not already present in the specified textElement list. %
% returns the position of the string in the text array %
integer procedure readString ( reference(textElement) value result txList; string(1) value terminator ) ; begin
string(256) str;
integer sLen, sPos, ePos;
logical found;
reference(textElement) txPos, txLastPos;
% get the text of the string %
str := " ";
sLen := 0;
str( sLen // 1 ) := line( lPos // 1 );
sLen := sLen + 1;
lPos := lPos + 1;
while lPos <= 255 and line( lPos // 1 ) not = terminator do begin
str( sLen // 1 ) := line( lPos // 1 );
sLen := sLen + 1;
lPos := lPos + 1
end while_more_string ;
if lPos > 255 then fatalError( tkLine, tkColumn, "Unterminated String in token file." );
% attempt to find the text in the list of strings/identifiers %
txLastPos := txPos := txList;
found := false;
ePos := 0;
while not found and txPos not = null do begin
ePos := ePos + 1;
found := ( length(txPos) = sLen );
sPos := 0;
while found and sPos < sLen do begin
found := str( sPos // 1 ) = text( start(txPos) + sPos );
sPos := sPos + 1
end while_not_found ;
txLastPos := txPos;
if not found then txPos := next(txPos)
end while_string_not_found ;
if not found then begin
% the string/identifier is not in the list - add it %
ePos := ePos + 1;
if txList = null then txList := textElement( textNext, sLen, null )
else next(txLastPos) := textElement( textNext, sLen, null );
if textNext + sLen > TEXT_MAX then fatalError( tkLine, tkColumn, "Text space exhausted." )
else begin
for cPos := 0 until sLen - 1 do begin
text( textNext ) := str( cPos // 1 );
textNext := textNext + 1
end for_cPos
end
end if_not_found ;
ePos
end readString ;
% gets an integer from the line - no checks for valid digits %
integer procedure readInteger ; begin
integer n;
while line( lPos // 1 ) = " " do lPos := lPos + 1;
n := 0;
while line( lPos // 1 ) not = " " do begin
n := ( n * 10 ) + ( decode( line( lPos // 1 ) ) - decode( "0" ) );
lPos := lPos + 1
end while_not_end_of_integer ;
n
end readInteger ;
string(256) line;
string(16) name;
integer lPos, tPos;
tPos := lPos := 0;
readcard( line );
% get the line and column numbers %
tkLine := readInteger;
tkColumn := readInteger;
% get the token name %
while line( lPos // 1 ) = " " do lPos := lPos + 1;
name := "";
while lPos < 256 and line( lPos // 1 ) not = " " do begin
name( tPos // 1 ) := line( lPos // 1 );
lPos := lPos + 1;
tPos := tPos + 1
end while_more_name ;
% determine the token type %
tkType := 1;
tkIntegerValue := 0;
while tkType <= MAX_TOKEN_TYPE and name not = tkName( tkType ) do tkType := tkType + 1;
if tkType > MAX_TOKEN_TYPE then fatalError( tkLine, tkColumn, "Malformed token" );
% handle the additional parameter for identifier/string/integer %
if tkType = tInteger or tkType = tIdentifier or tkType = tString then begin
while line( lPos // 1 ) = " " do lPos := lPos + 1;
if tkType = tInteger then tkIntegerValue := readInteger
else if tkType = tIdentifier then tkIntegerValue := readString( idList, " " )
else % tkType = tString % tkIntegerValue := readString( stList, """" )
end if_token_with_additional_parameter ;
end readToken ;
% parses a statement %
reference(node) procedure parseStatement ; begin
reference(node) stmtNode, stmtExpr;
% skips the current token if it is expectedToken, %
% returns true if the token was expectedToken, false otherwise %
logical procedure have ( integer value expectedToken ) ; begin
logical haveExpectedToken;
haveExpectedToken := ( tkType = expectedToken );
if haveExpectedToken and tkType not = tEnd_of_input then readToken;
haveExpectedToken
end have ;
% issues an error message and skips past the next semi-colon or to end of input %
procedure skipStatement ( string(80) value message ) ; begin
synError( tkLine, tkColumn, message );
while tkType not = tEnd_of_input and not have( tSemicolon ) do readToken
end skipStatement ;
% checks we have a semicolon, issues an error and skips the statement if not %
procedure mustBeEndOfStatement ; begin
if not have( tSemicolon ) then skipStatement( """;"" expected." )
end mustBeEndOfStatement ;
% skips the current token if it is "(" and issues an error if it isn't %
procedure mustBeLeftParen ; begin
if not have( tLeftParen ) then synError( tkLine, tkColumn, """("" expected." )
end % mustBeLeftParen % ;
% skips the current token if it is ")" and issues an error if it isn't %
procedure mustBeRightParen ; begin
if not have( tRightParen ) then synError( tkLine, tkColumn, """)"" expected." )
end % mustBeRightParen % ;
% gets the next token and parses an expression with the specified precedence %
reference(node) procedure nextAndparseExpr ( integer value precedence ) ; begin
readToken;
parseExpr( precedence )
end nextAndParseExpr ;
% parses an expression with the specified precedence %
% all operators are assumed to be left-associative %
reference(node) procedure parseExpr ( integer value precedence ) ; begin
% handles a single token primary %
reference(node) procedure simplePrimary ( integer value primaryNodeType ) ; begin
reference(node) primaryNode;
primaryNode := operandNode( primaryNodeType, tkIntegerValue );
readToken;
primaryNode
end simplePrimary ;
reference(node) exprNode;
if precedence < PRIMARY_PREC then begin
exprNode := parseExpr( precedence + 1 );
while tkPrec( tkType ) = precedence do begin
integer op;
op := tkNode( tkType );
exprNode := opNode( op, exprNode, nextAndParseExpr( precedence + 1 ) )
end while_op_at_this_precedence_level
end
else if tkType = tIdentifier then exprNode := simplePrimary( nIdentifier )
else if tkType = tInteger then exprNode := simplePrimary( nInteger )
else if tkType = nString then begin
synError( tkLine, tkColumn, "Unexpected string literal." );
exprNode := simplePrimary( nInteger )
end
else if tkType = tLeftParen then exprNode := parseParenExpr
else if tkType = tOp_add then exprNode := nextAndParseExpr( precedence )
else if tkType = tOp_subtract then exprNode := opNode( nNegate, nextAndParseExpr( precedence ), null )
else if tkType = tOp_not then exprNode := opNode( nNot, nextAndParseExpr( precedence ), null )
else begin
synError( tkLine, tkColumn, "Syntax error in expression." );
exprNode := simplePrimary( nInteger )
end;
exprNode
end parseExpr ;
% parses a preenthesised expression %
reference(node) procedure parseParenExpr ; begin
reference(node) exprNode;
mustBeLeftParen;
exprNode := parseExpr( 0 );
mustBeRightParen;
exprNode
end parseParenExpr ;
% parse statement depending on it's first token %
if tkType = tIdentifier then begin % assignment statement %
stmtExpr := operandNode( nIdentifier, tkIntegerValue );
% skip the identifier and check for "=" %
readToken;
if not have( tOp_Assign ) then synError( tkLine, tkColumn, "Expected ""="" in assignment statement." );
stmtNode := opNode( nAssign, stmtExpr, parseExpr( 0 ) );
mustBeEndOfStatement
end
else if have( tKeyword_while ) then begin
stmtExpr := parseParenExpr;
stmtNode := opNode( nWhile, stmtExpr, parseStatement )
end
else if have( tkeyword_if ) then begin
stmtExpr := parseParenExpr;
stmtNode := opNode( nIf, stmtExpr, opNode( nIf, parseStatement, null ) );
if have( tKeyword_else ) then % have an "else" part % right(right(stmtNode)) := parseStatement
end
else if have( tKeyword_Print ) then begin
mustBeLeftParen;
stmtNode := null;
while begin
if tkType = tString then begin
stmtNode := opNode( nSequence, stmtNode, opNode( nPrts, operandNode( nString, tkIntegerValue ), null ) );
readToken
end
else stmtNode := opNode( nSequence, stmtNode, opNode( nPrti, parseExpr( 0 ), null ) );
have( tComma )
end do begin end;
mustBeRightparen;
mustBeEndOfStatement;
end
else if have( tKeyword_Putc ) then begin
stmtNode := opNode( nPrtc, parseParenExpr, null );
mustBeEndOfStatement
end
else if have( tLeftBrace ) then begin % block %
stmtNode := parseStatementList( tRightBrace );
if not have( tRightBrace ) then synError( tkLine, tkColumn, "Expected ""}""." );
end
else if have( tSemicolon ) then stmtNode := null
else begin % unrecognised statement %
skipStatement( "Unrecognised statement." );
stmtNode := null
end if_various_tokens ;
stmtNode
end parseStatement ;
% parses a statement list ending with the specified terminator %
reference(node) procedure parseStatementList ( integer value terminator ) ; begin
reference(node) listNode;
listNode := null;
while tkType not = terminator and tkType not = tEnd_of_input do listNode := opNode( nSequence, listNode, parseStatement );
listNode
end parseStatementList ;
nIdentifier := 1; ndName( nIdentifier ) := "Identifier"; nString := 2; ndName( nString ) := "String";
nInteger := 3; ndName( nInteger ) := "Integer"; nSequence := 4; ndName( nSequence ) := "Sequence";
nIf := 5; ndName( nIf ) := "If"; nPrtc := 6; ndName( nPrtc ) := "Prtc";
nPrts := 7; ndName( nPrts ) := "Prts"; nPrti := 8; ndName( nPrti ) := "Prti";
nWhile := 9; ndName( nWhile ) := "While"; nAssign := 10; ndName( nAssign ) := "Assign";
nNegate := 11; ndName( nNegate ) := "Negate"; nNot := 12; ndName( nNot ) := "Not";
nMultiply := 13; ndName( nMultiply ) := "Multiply"; nDivide := 14; ndName( nDivide ) := "Divide";
nMod := 15; ndName( nMod ) := "Mod"; nAdd := 16; ndName( nAdd ) := "Add";
nSubtract := 17; ndName( nSubtract ) := "Subtract"; nLess := 18; ndName( nLess ) := "Less";
nLessEqual := 19; ndName( nLessEqual ) := "LessEqual" ; nGreater := 20; ndName( nGreater ) := "Greater";
nGreaterEqual := 21; ndName( nGreaterEqual ) := "GreaterEqual"; nEqual := 22; ndName( nEqual ) := "Equal";
nNotEqual := 23; ndName( nNotEqual ) := "NotEqual"; nAnd := 24; ndName( nAnd ) := "And";
nOr := 25; ndName( nOr ) := "Or";
tOp_multiply := 1; tkName( tOp_multiply ) := "Op_multiply"; tkPrec( tOp_multiply ) := 5;
tOp_divide := 2; tkName( tOp_divide ) := "Op_divide"; tkPrec( tOp_divide ) := 5;
tOp_mod := 3; tkName( tOp_mod ) := "Op_mod"; tkPrec( tOp_mod ) := 5;
tOp_add := 4; tkName( tOp_add ) := "Op_add"; tkPrec( tOp_add ) := 4;
tOp_subtract := 5; tkName( tOp_subtract ) := "Op_subtract"; tkPrec( tOp_subtract ) := 4;
tOp_negate := 6; tkName( tOp_negate ) := "Op_negate"; tkPrec( tOp_negate ) := -1;
tOp_less := 7; tkName( tOp_less ) := "Op_less"; tkPrec( tOp_less ) := 3;
tOp_lessequal := 8; tkName( tOp_lessequal ) := "Op_lessequal"; tkPrec( tOp_lessequal ) := 3;
tOp_greater := 9; tkName( tOp_greater ) := "Op_greater"; tkPrec( tOp_greater ) := 3;
tOp_greaterequal := 10; tkName( tOp_greaterequal ) := "Op_greaterequal"; tkPrec( tOp_greaterequal ) := 3;
tOp_equal := 11; tkName( tOp_equal ) := "Op_equal"; tkPrec( tOp_equal ) := 2;
tOp_notequal := 12; tkName( tOp_notequal ) := "Op_notequal"; tkPrec( tOp_notequal ) := 2;
tOp_not := 13; tkName( tOp_not ) := "Op_not"; tkPrec( tOp_not ) := -1;
tOp_assign := 14; tkName( tOp_assign ) := "Op_assign"; tkPrec( tOp_assign ) := -1;
tOp_and := 15; tkName( tOp_and ) := "Op_and"; tkPrec( tOp_and ) := 1;
tOp_or := 16; tkName( tOp_or ) := "Op_or"; tkPrec( tOp_or ) := 0;
tLeftParen := 17; tkName( tLeftParen ) := "LeftParen"; tkPrec( tLeftParen ) := -1;
tRightParen := 18; tkName( tRightParen ) := "RightParen"; tkPrec( tRightParen ) := -1;
tLeftBrace := 19; tkName( tLeftBrace ) := "LeftBrace"; tkPrec( tLeftBrace ) := -1;
tRightBrace := 20; tkName( tRightBrace ) := "RightBrace"; tkPrec( tRightBrace ) := -1;
tSemicolon := 21; tkName( tSemicolon ) := "Semicolon"; tkPrec( tSemicolon ) := -1;
tComma := 22; tkName( tComma ) := "Comma"; tkPrec( tComma ) := -1;
tKeyword_if := 23; tkName( tKeyword_if ) := "Keyword_if"; tkPrec( tKeyword_if ) := -1;
tKeyword_else := 24; tkName( tKeyword_else ) := "Keyword_else"; tkPrec( tKeyword_else ) := -1;
tKeyword_while := 25; tkName( tKeyword_while ) := "Keyword_while"; tkPrec( tKeyword_while ) := -1;
tKeyword_print := 26; tkName( tKeyword_print ) := "Keyword_print"; tkPrec( tKeyword_print ) := -1;
tKeyword_putc := 27; tkName( tKeyword_putc ) := "Keyword_putc"; tkPrec( tKeyword_putc ) := -1;
tIdentifier := 28; tkName( tIdentifier ) := "Identifier"; tkPrec( tIdentifier ) := -1;
tInteger := 29; tkName( tInteger ) := "Integer"; tkPrec( tInteger ) := -1;
tString := 30; tkName( tString ) := "String"; tkPrec( tString ) := -1;
tEnd_of_input := 31; tkName( tEnd_of_input ) := "End_of_input"; tkPrec( tEnd_of_input ) := -1;
MAX_TOKEN_TYPE := 31; TEXT_MAX := 4095; textNext := 0; PRIMARY_PREC := 6;
for tkPos := 1 until MAX_TOKEN_TYPE do tkNode( tkPos ) := - tkPos;
tkNode( tOp_multiply ) := nMultiply; tkNode( tOp_divide ) := nDivide; tkNode( tOp_mod ) := nMod;
tkNode( tOp_add ) := nAdd; tkNode( tOp_subtract ) := nSubtract; tkNode( tOp_less ) := nLess;
tkNode( tOp_lessequal ) := nLessEqual; tkNode( tOp_greater ) := nGreater; tkNode( tOp_greaterequal ) := nGreaterEqual;
tkNode( tOp_equal ) := nEqual; tkNode( tOp_notequal ) := nNotEqual; tkNode( tOp_not ) := nNot;
tkNode( tOp_and ) := nAnd; tkNode( tOp_or ) := nOr;
stList := idList := null;
% parse the output from the lexical analyser and output the linearised parse tree %
readToken;
writeNode( parseStatementList( tEnd_of_input ) )
end.
{{out}} Output from parsing the Prime Numbers example program.
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier count
Integer 1
Assign
Identifier n
Integer 1
Assign
Identifier limit
Integer 100
While
Less
Identifier n
Identifier limit
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier k
Integer 3
Assign
Identifier p
Integer 1
Assign
Identifier n
Add
Identifier n
Integer 2
While
And
LessEqual
Multiply
Identifier k
Identifier k
Identifier n
Identifier p
Sequence
Sequence
;
Assign
Identifier p
NotEqual
Multiply
Divide
Identifier n
Identifier k
Identifier k
Identifier n
Assign
Identifier k
Add
Identifier k
Integer 2
If
Identifier p
If
Sequence
Sequence
;
Sequence
Sequence
;
Prti
Identifier n
;
Prts
String " is prime\n"
;
Assign
Identifier count
Add
Identifier count
Integer 1
;
Sequence
Sequence
Sequence
;
Prts
String "Total primes found: "
;
Prti
Identifier count
;
Prts
String "\n"
;
AWK
Tested with gawk 4.1.1 and mawk 1.3.4.
function Token_assign(tk, attr, attr_array, n, i) {
n=split(attr, attr_array)
for(i=1; i<=n; i++)
Tokens[tk,i-1] = attr_array[i]
}
#*** show error and exit
function error(msg) {
printf("(%s, %s) %s\n", err_line, err_col, msg)
exit(1)
}
function gettok( line, n, i) {
getline line
if (line == "")
error("empty line")
n=split(line, line_list)
# line col Ident var_name
# 1 2 3 4
err_line = line_list[1]
err_col = line_list[2]
tok_text = line_list[3]
tok = all_syms[tok_text]
for (i=5; i<=n; i++)
line_list[4] = line_list[4] " " line_list[i]
if (tok == "")
error("Unknown token " tok_text)
tok_other = ""
if (tok == "tk_Integer" || tok == "tk_Ident" || tok =="tk_String")
tok_other = line_list[4]
}
function make_node(oper, left, right, value) {
node_type [next_free_node_index] = oper
node_left [next_free_node_index] = left
node_right[next_free_node_index] = right
node_value[next_free_node_index] = value
return next_free_node_index ++
}
function make_leaf(oper, n) {
return make_node(oper, 0, 0, n)
}
function expect(msg, s) {
if (tok == s) {
gettok()
return
}
error(msg ": Expecting '" Tokens[s,TK_NAME] "', found '" Tokens[tok,TK_NAME] "'")
}
function expr(p, x, op, node) {
x = 0
if (tok == "tk_Lparen") {
x = paren_expr()
} else if (tok == "tk_Sub" || tok == "tk_Add") {
if (tok == "tk_Sub")
op = "tk_Negate"
else
op = "tk_Add"
gettok()
node = expr(Tokens["tk_Negate",TK_PRECEDENCE]+0)
if (op == "tk_Negate")
x = make_node("nd_Negate", node)
else
x = node
} else if (tok == "tk_Not") {
gettok()
x = make_node("nd_Not", expr(Tokens["tk_Not",TK_PRECEDENCE]+0))
} else if (tok == "tk_Ident") {
x = make_leaf("nd_Ident", tok_other)
gettok()
} else if (tok == "tk_Integer") {
x = make_leaf("nd_Integer", tok_other)
gettok()
} else {
error("Expecting a primary, found: " Tokens[tok,TK_NAME])
}
while (((Tokens[tok,TK_IS_BINARY]+0) > 0) && ((Tokens[tok,TK_PRECEDENCE]+0) >= p)) {
op = tok
gettok()
q = Tokens[op,TK_PRECEDENCE]+0
if (! (Tokens[op,TK_RIGHT_ASSOC]+0 > 0))
q += 1
node = expr(q)
x = make_node(Tokens[op,TK_NODE], x, node)
}
return x
}
function paren_expr( node) {
expect("paren_expr", "tk_Lparen")
node = expr(0)
expect("paren_expr", "tk_Rparen")
return node
}
function stmt( t, e, s, s2, v) {
t = 0
if (tok == "tk_If") {
gettok()
e = paren_expr()
s = stmt()
s2 = 0
if (tok == "tk_Else") {
gettok()
s2 = stmt()
}
t = make_node("nd_If", e, make_node("nd_If", s, s2))
} else if (tok == "tk_Putc") {
gettok()
e = paren_expr()
t = make_node("nd_Prtc", e)
expect("Putc", "tk_Semi")
} else if (tok == "tk_Print") {
gettok()
expect("Print", "tk_Lparen")
while (1) {
if (tok == "tk_String") {
e = make_node("nd_Prts", make_leaf("nd_String", tok_other))
gettok()
} else {
e = make_node("nd_Prti", expr(0))
}
t = make_node("nd_Sequence", t, e)
if (tok != "tk_Comma")
break
gettok()
}
expect("Print", "tk_Rparen")
expect("Print", "tk_Semi")
} else if (tok == "tk_Semi") {
gettok()
} else if (tok == "tk_Ident") {
v = make_leaf("nd_Ident", tok_other)
gettok()
expect("assign", "tk_Assign")
e = expr(0)
t = make_node("nd_Assign", v, e)
expect("assign", "tk_Semi")
} else if (tok == "tk_While") {
gettok()
e = paren_expr()
s = stmt()
t = make_node("nd_While", e, s)
} else if (tok == "tk_Lbrace") {
gettok()
while (tok != "tk_Rbrace" && tok != "tk_EOI")
t = make_node("nd_Sequence", t, stmt())
expect("Lbrace", "tk_Rbrace")
} else if (tok == "tk_EOI") {
} else {
error("Expecting start of statement, found: " Tokens[tok,TK_NAME])
}
return t
}
function parse( t) {
t = 0 # None
gettok()
while (1) {
t = make_node("nd_Sequence", t, stmt())
if (tok == "tk_EOI" || t == 0)
break
}
return t
}
function prt_ast(t) {
if (t == 0) {
print(";")
} else {
printf("%-14s", Display_nodes[node_type[t]])
if ((node_type[t] == "nd_Ident") || (node_type[t] == "nd_Integer"))
printf("%s\n", node_value[t])
else if (node_type[t] == "nd_String") {
printf("%s\n", node_value[t])
} else {
print("")
prt_ast(node_left[t])
prt_ast(node_right[t])
}
}
}
BEGIN {
all_syms["End_of_input" ] = "tk_EOI"
all_syms["Op_multiply" ] = "tk_Mul"
all_syms["Op_divide" ] = "tk_Div"
all_syms["Op_mod" ] = "tk_Mod"
all_syms["Op_add" ] = "tk_Add"
all_syms["Op_subtract" ] = "tk_Sub"
all_syms["Op_negate" ] = "tk_Negate"
all_syms["Op_not" ] = "tk_Not"
all_syms["Op_less" ] = "tk_Lss"
all_syms["Op_lessequal" ] = "tk_Leq"
all_syms["Op_greater" ] = "tk_Gtr"
all_syms["Op_greaterequal" ] = "tk_Geq"
all_syms["Op_equal" ] = "tk_Eq"
all_syms["Op_notequal" ] = "tk_Neq"
all_syms["Op_assign" ] = "tk_Assign"
all_syms["Op_and" ] = "tk_And"
all_syms["Op_or" ] = "tk_Or"
all_syms["Keyword_if" ] = "tk_If"
all_syms["Keyword_else" ] = "tk_Else"
all_syms["Keyword_while" ] = "tk_While"
all_syms["Keyword_print" ] = "tk_Print"
all_syms["Keyword_putc" ] = "tk_Putc"
all_syms["LeftParen" ] = "tk_Lparen"
all_syms["RightParen" ] = "tk_Rparen"
all_syms["LeftBrace" ] = "tk_Lbrace"
all_syms["RightBrace" ] = "tk_Rbrace"
all_syms["Semicolon" ] = "tk_Semi"
all_syms["Comma" ] = "tk_Comma"
all_syms["Identifier" ] = "tk_Ident"
all_syms["Integer" ] = "tk_Integer"
all_syms["String" ] = "tk_String"
Display_nodes["nd_Ident" ] = "Identifier"
Display_nodes["nd_String" ] = "String"
Display_nodes["nd_Integer" ] = "Integer"
Display_nodes["nd_Sequence"] = "Sequence"
Display_nodes["nd_If" ] = "If"
Display_nodes["nd_Prtc" ] = "Prtc"
Display_nodes["nd_Prts" ] = "Prts"
Display_nodes["nd_Prti" ] = "Prti"
Display_nodes["nd_While" ] = "While"
Display_nodes["nd_Assign" ] = "Assign"
Display_nodes["nd_Negate" ] = "Negate"
Display_nodes["nd_Not" ] = "Not"
Display_nodes["nd_Mul" ] = "Multiply"
Display_nodes["nd_Div" ] = "Divide"
Display_nodes["nd_Mod" ] = "Mod"
Display_nodes["nd_Add" ] = "Add"
Display_nodes["nd_Sub" ] = "Subtract"
Display_nodes["nd_Lss" ] = "Less"
Display_nodes["nd_Leq" ] = "LessEqual"
Display_nodes["nd_Gtr" ] = "Greater"
Display_nodes["nd_Geq" ] = "GreaterEqual"
Display_nodes["nd_Eql" ] = "Equal"
Display_nodes["nd_Neq" ] = "NotEqual"
Display_nodes["nd_And" ] = "And"
Display_nodes["nd_Or" ] = "Or"
TK_NAME = 0
TK_RIGHT_ASSOC = 1
TK_IS_BINARY = 2
TK_IS_UNARY = 3
TK_PRECEDENCE = 4
TK_NODE = 5
Token_assign("tk_EOI" , "EOI 0 0 0 -1 -1 ")
Token_assign("tk_Mul" , "* 0 1 0 13 nd_Mul ")
Token_assign("tk_Div" , "/ 0 1 0 13 nd_Div ")
Token_assign("tk_Mod" , "% 0 1 0 13 nd_Mod ")
Token_assign("tk_Add" , "+ 0 1 0 12 nd_Add ")
Token_assign("tk_Sub" , "- 0 1 0 12 nd_Sub ")
Token_assign("tk_Negate" , "- 0 0 1 14 nd_Negate ")
Token_assign("tk_Not" , "! 0 0 1 14 nd_Not ")
Token_assign("tk_Lss" , "< 0 1 0 10 nd_Lss ")
Token_assign("tk_Leq" , "<= 0 1 0 10 nd_Leq ")
Token_assign("tk_Gtr" , "> 0 1 0 10 nd_Gtr ")
Token_assign("tk_Geq" , ">= 0 1 0 10 nd_Geq ")
Token_assign("tk_Eql" , "== 0 1 0 9 nd_Eql ")
Token_assign("tk_Neq" , "!= 0 1 0 9 nd_Neq ")
Token_assign("tk_Assign" , "= 0 0 0 -1 nd_Assign ")
Token_assign("tk_And" , "&& 0 1 0 5 nd_And ")
Token_assign("tk_Or" , "|| 0 1 0 4 nd_Or ")
Token_assign("tk_If" , "if 0 0 0 -1 nd_If ")
Token_assign("tk_Else" , "else 0 0 0 -1 -1 ")
Token_assign("tk_While" , "while 0 0 0 -1 nd_While ")
Token_assign("tk_Print" , "print 0 0 0 -1 -1 ")
Token_assign("tk_Putc" , "putc 0 0 0 -1 -1 ")
Token_assign("tk_Lparen" , "( 0 0 0 -1 -1 ")
Token_assign("tk_Rparen" , ") 0 0 0 -1 -1 ")
Token_assign("tk_Lbrace" , "{ 0 0 0 -1 -1 ")
Token_assign("tk_Rbrace" , "} 0 0 0 -1 -1 ")
Token_assign("tk_Semi" , "; 0 0 0 -1 -1 ")
Token_assign("tk_Comma" , ", 0 0 0 -1 -1 ")
Token_assign("tk_Ident" , "Ident 0 0 0 -1 nd_Ident ")
Token_assign("tk_Integer", "Integer 0 0 0 -1 nd_Integer")
Token_assign("tk_String" , "String 0 0 0 -1 nd_String ")
input_file = "-"
err_line = 0
err_col = 0
tok = ""
tok_text = ""
next_free_node_index = 1
if (ARGC > 1)
input_file = ARGV[1]
t = parse()
prt_ast(t)
}
{{out|case=count}}
Sequence
Sequence
;
Assign
Identifier count
Integer 1
While
Less
Identifier count
Integer 10
Sequence
Sequence
;
Sequence
Sequence
Sequence
;
Prts
String "count is: "
;
Prti
Identifier count
;
Prts
String "\n"
;
Assign
Identifier count
Add
Identifier count
Integer 1
C
Tested with gcc 4.81 and later, compiles warning free with -Wall -Wextra
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <stdbool.h>
#include <ctype.h>
#define NELEMS(arr) (sizeof(arr) / sizeof(arr[0]))
typedef enum {
tk_EOI, tk_Mul, tk_Div, tk_Mod, tk_Add, tk_Sub, tk_Negate, tk_Not, tk_Lss, tk_Leq, tk_Gtr,
tk_Geq, tk_Eql, tk_Neq, tk_Assign, tk_And, tk_Or, tk_If, tk_Else, tk_While, tk_Print,
tk_Putc, tk_Lparen, tk_Rparen, tk_Lbrace, tk_Rbrace, tk_Semi, tk_Comma, tk_Ident,
tk_Integer, tk_String
} TokenType;
typedef enum {
nd_Ident, nd_String, nd_Integer, nd_Sequence, nd_If, nd_Prtc, nd_Prts, nd_Prti, nd_While,
nd_Assign, nd_Negate, nd_Not, nd_Mul, nd_Div, nd_Mod, nd_Add, nd_Sub, nd_Lss, nd_Leq,
nd_Gtr, nd_Geq, nd_Eql, nd_Neq, nd_And, nd_Or
} NodeType;
typedef struct {
TokenType tok;
int err_ln;
int err_col;
char *text; /* ident or string literal or integer value */
} tok_s;
typedef struct Tree {
NodeType node_type;
struct Tree *left;
struct Tree *right;
char *value;
} Tree;
// dependency: Ordered by tok, must remain in same order as TokenType enum
struct {
char *text, *enum_text;
TokenType tok;
bool right_associative, is_binary, is_unary;
int precedence;
NodeType node_type;
} atr[] = {
{"EOI", "End_of_input" , tk_EOI, false, false, false, -1, -1 },
{"*", "Op_multiply" , tk_Mul, false, true, false, 13, nd_Mul },
{"/", "Op_divide" , tk_Div, false, true, false, 13, nd_Div },
{"%", "Op_mod" , tk_Mod, false, true, false, 13, nd_Mod },
{"+", "Op_add" , tk_Add, false, true, false, 12, nd_Add },
{"-", "Op_subtract" , tk_Sub, false, true, false, 12, nd_Sub },
{"-", "Op_negate" , tk_Negate, false, false, true, 14, nd_Negate },
{"!", "Op_not" , tk_Not, false, false, true, 14, nd_Not },
{"<", "Op_less" , tk_Lss, false, true, false, 10, nd_Lss },
{"<=", "Op_lessequal" , tk_Leq, false, true, false, 10, nd_Leq },
{">", "Op_greater" , tk_Gtr, false, true, false, 10, nd_Gtr },
{">=", "Op_greaterequal", tk_Geq, false, true, false, 10, nd_Geq },
{"==", "Op_equal" , tk_Eql, false, true, false, 9, nd_Eql },
{"!=", "Op_notequal" , tk_Neq, false, true, false, 9, nd_Neq },
{"=", "Op_assign" , tk_Assign, false, false, false, -1, nd_Assign },
{"&&", "Op_and" , tk_And, false, true, false, 5, nd_And },
{"||", "Op_or" , tk_Or, false, true, false, 4, nd_Or },
{"if", "Keyword_if" , tk_If, false, false, false, -1, nd_If },
{"else", "Keyword_else" , tk_Else, false, false, false, -1, -1 },
{"while", "Keyword_while" , tk_While, false, false, false, -1, nd_While },
{"print", "Keyword_print" , tk_Print, false, false, false, -1, -1 },
{"putc", "Keyword_putc" , tk_Putc, false, false, false, -1, -1 },
{"(", "LeftParen" , tk_Lparen, false, false, false, -1, -1 },
{")", "RightParen" , tk_Rparen, false, false, false, -1, -1 },
{"{", "LeftBrace" , tk_Lbrace, false, false, false, -1, -1 },
{"}", "RightBrace" , tk_Rbrace, false, false, false, -1, -1 },
{";", "Semicolon" , tk_Semi, false, false, false, -1, -1 },
{",", "Comma" , tk_Comma, false, false, false, -1, -1 },
{"Ident", "Identifier" , tk_Ident, false, false, false, -1, nd_Ident },
{"Integer literal", "Integer" , tk_Integer, false, false, false, -1, nd_Integer},
{"String literal", "String" , tk_String, false, false, false, -1, nd_String },
};
char *Display_nodes[] = {"Identifier", "String", "Integer", "Sequence", "If", "Prtc",
"Prts", "Prti", "While", "Assign", "Negate", "Not", "Multiply", "Divide", "Mod",
"Add", "Subtract", "Less", "LessEqual", "Greater", "GreaterEqual", "Equal",
"NotEqual", "And", "Or"};
static tok_s tok;
static FILE *source_fp, *dest_fp;
Tree *paren_expr();
void error(int err_line, int err_col, const char *fmt, ... ) {
va_list ap;
char buf[1000];
va_start(ap, fmt);
vsprintf(buf, fmt, ap);
va_end(ap);
printf("(%d, %d) error: %s\n", err_line, err_col, buf);
exit(1);
}
char *read_line(int *len) {
static char *text = NULL;
static int textmax = 0;
for (*len = 0; ; (*len)++) {
int ch = fgetc(source_fp);
if (ch == EOF || ch == '\n') {
if (*len == 0)
return NULL;
break;
}
if (*len + 1 >= textmax) {
textmax = (textmax == 0 ? 128 : textmax * 2);
text = realloc(text, textmax);
}
text[*len] = ch;
}
text[*len] = '\0';
return text;
}
char *rtrim(char *text, int *len) { // remove trailing spaces
for (; *len > 0 && isspace(text[*len - 1]); --(*len))
;
text[*len] = '\0';
return text;
}
TokenType get_enum(const char *name) { // return internal version of name
for (size_t i = 0; i < NELEMS(atr); i++) {
if (strcmp(atr[i].enum_text, name) == 0)
return atr[i].tok;
}
error(0, 0, "Unknown token %s\n", name);
return 0;
}
tok_s gettok() {
int len;
tok_s tok;
char *yytext = read_line(&len);
yytext = rtrim(yytext, &len);
// [ ]*{lineno}[ ]+{colno}[ ]+token[ ]+optional
// get line and column
tok.err_ln = atoi(strtok(yytext, " "));
tok.err_col = atoi(strtok(NULL, " "));
// get the token name
char *name = strtok(NULL, " ");
tok.tok = get_enum(name);
// if there is extra data, get it
char *p = name + strlen(name);
if (p != &yytext[len]) {
for (++p; isspace(*p); ++p)
;
tok.text = strdup(p);
}
return tok;
}
Tree *make_node(NodeType node_type, Tree *left, Tree *right) {
Tree *t = calloc(sizeof(Tree), 1);
t->node_type = node_type;
t->left = left;
t->right = right;
return t;
}
Tree *make_leaf(NodeType node_type, char *value) {
Tree *t = calloc(sizeof(Tree), 1);
t->node_type = node_type;
t->value = strdup(value);
return t;
}
void expect(const char msg[], TokenType s) {
if (tok.tok == s) {
tok = gettok();
return;
}
error(tok.err_ln, tok.err_col, "%s: Expecting '%s', found '%s'\n", msg, atr[s].text, atr[tok.tok].text);
}
Tree *expr(int p) {
Tree *x = NULL, *node;
TokenType op;
switch (tok.tok) {
case tk_Lparen:
x = paren_expr();
break;
case tk_Sub: case tk_Add:
op = tok.tok;
tok = gettok();
node = expr(atr[tk_Negate].precedence);
x = (op == tk_Sub) ? make_node(nd_Negate, node, NULL) : node;
break;
case tk_Not:
tok = gettok();
x = make_node(nd_Not, expr(atr[tk_Not].precedence), NULL);
break;
case tk_Ident:
x = make_leaf(nd_Ident, tok.text);
tok = gettok();
break;
case tk_Integer:
x = make_leaf(nd_Integer, tok.text);
tok = gettok();
break;
default:
error(tok.err_ln, tok.err_col, "Expecting a primary, found: %s\n", atr[tok.tok].text);
}
while (atr[tok.tok].is_binary && atr[tok.tok].precedence >= p) {
TokenType op = tok.tok;
tok = gettok();
int q = atr[op].precedence;
if (!atr[op].right_associative)
q++;
node = expr(q);
x = make_node(atr[op].node_type, x, node);
}
return x;
}
Tree *paren_expr() {
expect("paren_expr", tk_Lparen);
Tree *t = expr(0);
expect("paren_expr", tk_Rparen);
return t;
}
Tree *stmt() {
Tree *t = NULL, *v, *e, *s, *s2;
switch (tok.tok) {
case tk_If:
tok = gettok();
e = paren_expr();
s = stmt();
s2 = NULL;
if (tok.tok == tk_Else) {
tok = gettok();
s2 = stmt();
}
t = make_node(nd_If, e, make_node(nd_If, s, s2));
break;
case tk_Putc:
tok = gettok();
e = paren_expr();
t = make_node(nd_Prtc, e, NULL);
expect("Putc", tk_Semi);
break;
case tk_Print: /* print '(' expr {',' expr} ')' */
tok = gettok();
for (expect("Print", tk_Lparen); ; expect("Print", tk_Comma)) {
if (tok.tok == tk_String) {
e = make_node(nd_Prts, make_leaf(nd_String, tok.text), NULL);
tok = gettok();
} else
e = make_node(nd_Prti, expr(0), NULL);
t = make_node(nd_Sequence, t, e);
if (tok.tok != tk_Comma)
break;
}
expect("Print", tk_Rparen);
expect("Print", tk_Semi);
break;
case tk_Semi:
tok = gettok();
break;
case tk_Ident:
v = make_leaf(nd_Ident, tok.text);
tok = gettok();
expect("assign", tk_Assign);
e = expr(0);
t = make_node(nd_Assign, v, e);
expect("assign", tk_Semi);
break;
case tk_While:
tok = gettok();
e = paren_expr();
s = stmt();
t = make_node(nd_While, e, s);
break;
case tk_Lbrace: /* {stmt} */
for (expect("Lbrace", tk_Lbrace); tok.tok != tk_Rbrace && tok.tok != tk_EOI;)
t = make_node(nd_Sequence, t, stmt());
expect("Lbrace", tk_Rbrace);
break;
case tk_EOI:
break;
default: error(tok.err_ln, tok.err_col, "expecting start of statement, found '%s'\n", atr[tok.tok].text);
}
return t;
}
Tree *parse() {
Tree *t = NULL;
tok = gettok();
do {
t = make_node(nd_Sequence, t, stmt());
} while (t != NULL && tok.tok != tk_EOI);
return t;
}
void prt_ast(Tree *t) {
if (t == NULL)
printf(";\n");
else {
printf("%-14s ", Display_nodes[t->node_type]);
if (t->node_type == nd_Ident || t->node_type == nd_Integer || t->node_type == nd_String) {
printf("%s\n", t->value);
} else {
printf("\n");
prt_ast(t->left);
prt_ast(t->right);
}
}
}
void init_io(FILE **fp, FILE *std, const char mode[], const char fn[]) {
if (fn[0] == '\0')
*fp = std;
else if ((*fp = fopen(fn, mode)) == NULL)
error(0, 0, "Can't open %s\n", fn);
}
int main(int argc, char *argv[]) {
init_io(&source_fp, stdin, "r", argc > 1 ? argv[1] : "");
init_io(&dest_fp, stdout, "wb", argc > 2 ? argv[2] : "");
prt_ast(parse());
}
{{out|case=prime numbers AST}}
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier count
Integer 1
Assign
Identifier n
Integer 1
Assign
Identifier limit
Integer 100
While
Less
Identifier n
Identifier limit
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier k
Integer 3
Assign
Identifier p
Integer 1
Assign
Identifier n
Add
Identifier n
Integer 2
While
And
LessEqual
Multiply
Identifier k
Identifier k
Identifier n
Identifier p
Sequence
Sequence
;
Assign
Identifier p
NotEqual
Multiply
Divide
Identifier n
Identifier k
Identifier k
Identifier n
Assign
Identifier k
Add
Identifier k
Integer 2
If
Identifier p
If
Sequence
Sequence
;
Sequence
Sequence
;
Prti
Identifier n
;
Prts
String " is prime\n"
;
Assign
Identifier count
Add
Identifier count
Integer 1
;
Sequence
Sequence
Sequence
;
Prts
String "Total primes found: "
;
Prti
Identifier count
;
Prts
String "\n"
;
COBOL
Code by Steve Williams. Tested with GnuCOBOL 2.2.
SOURCE FORMAT IS FREE
identification division.
*> this code is dedicated to the public domain
*> (GnuCOBOL) 2.3-dev.0
*> for extra credit, generate this program directly from the EBNF
program-id. parser.
environment division.
configuration section.
repository. function all intrinsic.
input-output section.
file-control.
select input-file assign using input-name
status is input-status
organization is line sequential.
data division.
file section.
fd input-file global.
01 input-record global.
03 input-line pic zzzz9.
03 input-column pic zzzzzz9.
03 filler pic x(3).
03 input-token pic x(16).
03 input-value pic x(48).
working-storage section.
01 program-name pic x(32) value spaces global.
01 input-name pic x(32) value spaces global.
01 input-status pic xx global.
01 line-no pic 999 value 0.
01 col-no pic 99 value 0.
01 error-record global.
03 error-line-no pic zzzz9.
03 error-col-no pic zzzzzz9.
03 filler pic x value space.
03 error-message pic x(64) value spaces.
01 token global.
03 token-type pic x(16).
03 token-line pic 999.
03 token-column pic 99.
03 token-value pic x(48).
01 parse-stack global.
03 p pic 999 value 0.
03 p-lim pic 999 value 200.
03 p-zero pic 999 value 0.
03 parse-entry occurs 200.
05 parse-name pic x(24).
05 parse-token pic x(16).
05 parse-left pic 999.
05 parse-right pic 999.
05 parse-work pic 999.
05 parse-work1 pic 999.
01 abstract-syntax-tree global.
03 t pic 999 value 0.
03 t1 pic 999.
03 t-lim pic 999 value 998.
03 filler occurs 998.
05 leaf.
07 leaf-type pic x(14).
07 leaf-value pic x(48).
05 node redefines leaf.
07 node-type pic x(14).
07 node-left pic 999.
07 node-right pic 999.
01 indent pic x(200) value all '| ' global.
procedure division chaining program-name.
start-parser.
if program-name <> spaces
string program-name delimited by space '.lex' into input-name
open input input-file
if input-status <> '00'
string 'in parser ' trim(input-name) ' open status ' input-status
into error-message
call 'reporterror'
end-if
end-if
call 'gettoken'
call 'stmt_list'
if input-name <> spaces
close input-file
end-if
call 'printast' using t
>>d perform dump-ast
stop run
.
dump-ast.
display '
### ====
' upon syserr
display 'ast:' upon syserr
display 't=' t upon syserr
perform varying t1 from 1 by 1 until t1 > t
if leaf-type(t1) = 'Identifier' or 'Integer' or 'String'
display t1 space trim(leaf-type(t1)) space trim(leaf-value(t1)) upon syserr
else
display t1 space node-left(t1) space node-right(t1) space trim(node-type(t1))
upon syserr
end-if
end-perform
.
identification division.
program-id. stmt_list common recursive.
data division.
procedure division.
start-stmt_list.
call 'push' using module-id
move p-zero to parse-left(p)
perform forever
call 'stmt'
move return-code to parse-right(p)
call 'makenode' using 'Sequence' parse-left(p) parse-right(p)
move return-code to parse-left(p)
if parse-right(p) = 0
or token-type = 'End_of_input'
exit perform
end-if
end-perform
call 'pop'
.
end program stmt_list.
identification division.
program-id. stmt common recursive.
procedure division.
start-stmt.
call 'push' using module-id
move p-zero to parse-left(p)
evaluate token-type
when 'Semicolon'
call 'gettoken'
when 'Identifier'
*>Identifier '=' expr ';'
call 'makeleaf' using 'Identifier' token-value
move return-code to parse-left(p)
call 'gettoken'
call 'expect' using 'Op_assign'
call 'expr'
move return-code to parse-right(p)
call 'expect' using 'Semicolon'
call 'makenode' using 'Assign' parse-left(p) parse-right(p)
move return-code to parse-left(p)
when 'Keyword_while'
*>'while' paren_expr '{' stmt '}'
call 'gettoken'
call 'paren_expr'
move return-code to parse-work(p)
call 'stmt'
move return-code to parse-right(p)
call 'makenode' using 'While' parse-work(p) parse-right(p)
move return-code to parse-left(p)
when 'Keyword_if'
*>'if' paren_expr stmt ['else' stmt]
call 'gettoken'
call 'paren_expr'
move return-code to parse-left(p)
call 'stmt'
move return-code to parse-work(p)
move p-zero to parse-work1(p)
if token-type = 'Keyword_else'
call 'gettoken'
call 'stmt'
move return-code to parse-work1(p)
end-if
call 'makenode' using 'If' parse-work(p) parse-work1(p)
move return-code to parse-right(p)
call 'makenode' using 'If' parse-left(p) parse-right(p)
move return-code to parse-left(p)
when 'Keyword_print'
*>'print' '(' prt_list ')' ';'
call 'gettoken'
call 'expect' using 'LeftParen'
call 'prt_list'
move return-code to parse-left(p)
call 'expect' using 'RightParen'
call 'expect' using 'Semicolon'
when 'Keyword_putc'
*>'putc' paren_expr ';'
call 'gettoken'
call 'paren_expr'
move return-code to parse-left(p)
call 'makenode' using 'Prtc' parse-left(p) p-zero
move return-code to parse-left(p)
call 'expect' using 'Semicolon'
when 'LeftBrace'
*>'{' stmt '}'
call 'gettoken'
move p-zero to parse-left(p)
perform until token-type = 'RightBrace' or 'End_of_input'
call 'stmt'
move return-code to parse-right(p)
call 'makenode' using 'Sequence' parse-left(p) parse-right(p)
move return-code to parse-left(p)
end-perform
if token-type <> 'End_of_input'
call 'gettoken'
end-if
when other
move 0 to parse-left(p)
end-evaluate
move parse-left(p) to return-code
call 'pop'
.
end program stmt.
identification division.
program-id. paren_expr common recursive.
procedure division.
start-paren_expr.
*>'(' expr ')' ;
call 'push' using module-id
call 'expect' using 'LeftParen'
call 'expr'
call 'expect' using 'RightParen'
call 'pop'
.
end program paren_expr.
identification division.
program-id. prt_list common.
procedure division.
start-prt_list.
*>(string | expr) {',' (String | expr)} ;
call 'push' using module-id
move p-zero to parse-work(p)
perform prt_entry
perform until token-type <> 'Comma'
call 'gettoken'
perform prt_entry
end-perform
call 'pop'
exit program
.
prt_entry.
if token-type = 'String'
call 'makeleaf' using token-type token-value
move return-code to parse-left(p)
call 'makenode' using 'Prts' parse-left(p) p-zero
call 'gettoken'
else
call 'expr'
move return-code to parse-left(p)
call 'makenode' using 'Prti' parse-left(p) p-zero
end-if
move return-code to parse-right(p)
call 'makenode' using 'Sequence' parse-work(p) parse-right(p)
move return-code to parse-work(p)
.
end program prt_list.
identification division.
program-id. expr common recursive.
procedure division.
start-expr.
*>and_expr {'||' and_expr} ;
call 'push' using module-id
call 'and_expr'
move return-code to parse-left(p)
perform forever
if token-type <> 'Op_or'
exit perform
end-if
call 'gettoken'
call 'and_expr'
move return-code to parse-right(p)
call 'makenode' using 'Or' parse-left(p) parse-right(p)
move return-code to parse-left(p)
end-perform
move parse-left(p) to return-code
call 'pop'
.
end program expr.
identification division.
program-id. and_expr common recursive.
procedure division.
start-and_expr.
*>equality_expr {'&&' equality_expr} ;
call 'push' using module-id
call 'equality_expr'
move return-code to parse-left(p)
perform forever
if token-type <> 'Op_and'
exit perform
end-if
call 'gettoken'
call 'equality_expr'
move return-code to parse-right(p)
call 'makenode' using 'And' parse-left(p) parse-right(p)
move return-code to parse-left(p)
end-perform
call 'pop'
.
end program and_expr.
identification division.
program-id. equality_expr common recursive.
procedure division.
start-equality_expr.
*>relational_expr [('==' | '!=') relational_expr] ;
call 'push' using module-id
call 'relational_expr'
move return-code to parse-left(p)
evaluate token-type
when 'Op_equal'
move 'Equal' to parse-token(p)
when 'Op_notequal'
move 'NotEqual' to parse-token(p)
end-evaluate
if parse-token(p) <> spaces
call 'gettoken'
call 'relational_expr'
move return-code to parse-right(p)
call 'makenode' using parse-token(p) parse-left(p) parse-right(p)
move return-code to parse-left(p)
end-if
call 'pop'
.
end program equality_expr.
identification division.
program-id. relational_expr common recursive.
procedure division.
start-relational_expr.
*>addition_expr [('<' | '<=' | '>' | '>=') addition_expr] ;
call 'push' using module-id
call 'addition_expr'
move return-code to parse-left(p)
evaluate token-type
when 'Op_less'
move 'Less' to parse-token(p)
when 'Op_lessequal'
move 'LessEqual' to parse-token(p)
when 'Op_greater'
move 'Greater' to parse-token(p)
when 'Op_greaterequal'
move 'GreaterEqual' to parse-token(p)
end-evaluate
if parse-token(p) <> spaces
call 'gettoken'
call 'addition_expr'
move return-code to parse-right(p)
call 'makenode' using parse-token(p) parse-left(p) parse-right(p)
move return-code to parse-left(p)
end-if
call 'pop'
.
end program relational_expr.
identification division.
program-id. addition_expr common recursive.
procedure division.
start-addition_expr.
*>multiplication_expr {('+' | '-') multiplication_expr} ;
call 'push' using module-id
call 'multiplication_expr'
move return-code to parse-left(p)
perform forever
evaluate token-type
when 'Op_add'
move 'Add' to parse-token(p)
when 'Op_subtract'
move 'Subtract' to parse-token(p)
when other
exit perform
end-evaluate
call 'gettoken'
call 'multiplication_expr'
move return-code to parse-right(p)
call 'makenode' using parse-token(p) parse-left(p) parse-right(p)
move return-code to parse-left(p)
end-perform
call 'pop'
.
end program addition_expr.
identification division.
program-id. multiplication_expr common recursive.
procedure division.
start-multiplication_expr.
*>primary {('*' | '/' | '%') primary } ;
call 'push' using module-id
call 'primary'
move return-code to parse-left(p)
perform forever
evaluate token-type
when 'Op_multiply'
move 'Multiply' to parse-token(p)
when 'Op_divide'
move 'Divide' to parse-token(p)
when 'Op_mod'
move 'Mod' to parse-token(p)
when other
exit perform
end-evaluate
call 'gettoken'
call 'primary'
move return-code to parse-right(p)
call 'makenode' using parse-token(p) parse-left(p) parse-right(p)
move return-code to parse-left(p)
end-perform
call 'pop'
.
end program multiplication_expr.
identification division.
program-id. primary common recursive.
procedure division.
start-primary.
*> Identifier
*>| Integer
*>| 'LeftParen' expr 'RightParen'
*>| ('+' | '-' | '!') primary
*>;
call 'push' using module-id
evaluate token-type
when 'Identifier'
call 'makeleaf' using 'Identifier' token-value
call 'gettoken'
when 'Integer'
call 'makeleaf' using 'Integer' token-value
call 'gettoken'
when 'LeftParen'
call 'gettoken'
call 'expr'
call 'expect' using 'RightParen'
move t to return-code
when 'Op_add'
call 'gettoken'
call 'primary'
when 'Op_subtract'
call 'gettoken'
call 'primary'
move return-code to parse-left(p)
call 'makenode' using 'Negate' parse-left(p) p-zero
when 'Op_not'
call 'gettoken'
call 'primary'
move return-code to parse-left(p)
call 'makenode' using 'Not' parse-left(p) p-zero
when other
move 0 to return-code
end-evaluate
call 'pop'
.
end program primary.
program-id. reporterror common.
procedure division.
start-reporterror.
report-error.
move token-line to error-line-no
move token-column to error-col-no
display error-record upon syserr
stop run with error status -1
.
end program reporterror.
identification division.
program-id. gettoken common.
procedure division.
start-gettoken.
if program-name = spaces
move '00' to input-status
accept input-record on exception move '10' to input-status end-accept
else
read input-file
end-if
evaluate input-status
when '00'
move input-token to token-type
move input-value to token-value
move numval(input-line) to token-line
move numval(input-column) to token-column
>>d display indent(1:min(4 * p,length(indent))) 'new token: ' token-type upon syserr
when '10'
string 'in parser ' trim(input-name) ' unexpected end of input'
into error-message
call 'reporterror'
when other
string 'in parser ' trim(input-name) ' unexpected input-status ' input-status
into error-message
call 'reporterror'
end-evaluate
.
end program gettoken.
identification division.
program-id. expect common.
data division.
linkage section.
01 what any length.
procedure division using what.
start-expect.
if token-type <> what
string 'in parser expected ' what ' found ' token-type into error-message
call 'reporterror'
end-if
>>d display indent(1:min(4 * p,length(indent))) 'match: ' token-type upon syserr
call 'gettoken'
.
end program expect.
identification division.
program-id. push common.
data division.
linkage section.
01 what any length.
procedure division using what.
start-push.
>>d display indent(1:min(4 * p,length(indent))) 'push ' what upon syserr
if p >= p-lim
move 'in parser stack overflow' to error-message
call 'reporterror'
end-if
add 1 to p
initialize parse-entry(p)
move what to parse-name(p)
.
end program push.
identification division.
program-id. pop common.
procedure division.
start-pop.
if p < 1
move 'in parser stack underflow' to error-message
call 'reporterror'
end-if
>>d display indent(1:4 * p - 4) 'pop ' parse-name(p) upon syserr
subtract 1 from p
.
end program pop.
identification division.
program-id. makenode common.
data division.
linkage section.
01 parm-type any length.
01 parm-left pic 999.
01 parm-right pic 999.
procedure division using parm-type parm-left parm-right.
start-makenode.
if t >= t-lim
string 'in parser makenode tree index t exceeds ' t-lim into error-message
call 'reporterror'
end-if
add 1 to t
move parm-type to node-type(t)
move parm-left to node-left(t)
move parm-right to node-right(t)
move t to return-code
.
end program makenode.
identification division.
program-id. makeleaf common.
data division.
linkage section.
01 parm-type any length.
01 parm-value pic x(48).
procedure division using parm-type parm-value.
start-makeleaf.
if t >= t-lim
string 'in parser makeleaf tree index t exceeds ' t-lim into error-message
call 'reporterror'
end-if
add 1 to t
move parm-type to leaf-type(t)
move parm-value to leaf-value(t)
move t to return-code
.
end program makeleaf.
identification division.
program-id. printast recursive.
data division.
linkage section.
01 n pic 999.
procedure division using n.
start-printast.
if n = 0
display ';'
exit program
end-if
evaluate leaf-type(n)
when 'Identifier'
when 'Integer'
when 'String'
display leaf-type(n) trim(leaf-value(n))
when other
display node-type(n)
call 'printast' using node-left(n)
call 'printast' using node-right(n)
end-evaluate
.
end program printast.
end program parser.
{{out|case=Primes}}
prompt$ ./lexer <testcases/Primes | ./parser
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier count
Integer 1
Assign
Identifier n
Integer 1
Assign
Identifier limit
Integer 100
While
Less
Identifier n
Identifier limit
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier k
Integer 3
Assign
Identifier p
Integer 1
Assign
Identifier n
Add
Identifier n
Integer 2
While
And
LessEqual
Multiply
Identifier k
Identifier k
Identifier n
Identifier p
Sequence
Sequence
;
Assign
Identifier p
NotEqual
Multiply
Divide
Identifier n
Identifier k
Identifier k
Identifier n
Assign
Identifier k
Add
Identifier k
Integer 2
If
Identifier p
If
Sequence
Sequence
;
Sequence
Sequence
;
Prti
Identifier n
;
Prts
String " is prime\n"
;
Assign
Identifier count
Add
Identifier count
Integer 1
;
Sequence
Sequence
Sequence
;
Prts
String "Total primes found: "
;
Prti
Identifier count
;
Prts
String "\n"
;
Forth
Tested with Gforth 0.7.3.
CREATE BUF 0 , \ single-character look-ahead buffer
: PEEK BUF @ 0= IF KEY BUF ! THEN BUF @ ;
: GETC PEEK 0 BUF ! ;
: SPACE? DUP BL = SWAP 9 14 WITHIN OR ;
: >SPACE BEGIN PEEK SPACE? WHILE GETC DROP REPEAT ;
: DIGIT? 48 58 WITHIN ;
: GETINT >SPACE 0
BEGIN PEEK DIGIT?
WHILE GETC [CHAR] 0 - SWAP 10 * +
REPEAT ;
: GETNAM >SPACE PAD 1+
BEGIN PEEK SPACE? INVERT
WHILE GETC OVER C! CHAR+
REPEAT PAD TUCK - 1- PAD C! ;
: GETSTR >SPACE PAD 1+ GETC DROP \ skip leading "
BEGIN GETC DUP [CHAR] " <>
WHILE OVER C! CHAR+
REPEAT DROP PAD TUCK - 1- PAD C! ;
: INTERN HERE SWAP DUP C@ 1+ BOUNDS DO I C@ C, LOOP ALIGN ;
CREATE #TK 0 ,
: TK: CREATE #TK @ , 1 #TK +! DOES> @ ;
TK: End_of_input TK: Keyword_if TK: Keyword_else
TK: Keyword_while TK: Keyword_print TK: Keyword_putc
TK: String TK: Integer TK: Identifier
TK: LeftParen TK: RightParen
TK: LeftBrace TK: RightBrace
TK: Semicolon TK: Comma
TK: Op_assign TK: Op_not
: (BINARY?) [ #TK @ ] literal >= ;
TK: Op_subtract TK: Op_add
TK: Op_mod TK: Op_multiply TK: Op_divide
TK: Op_equal TK: Op_notequal
TK: Op_less TK: Op_lessequal
TK: Op_greater TK: Op_greaterequal
TK: Op_and TK: Op_or
CREATE TOKEN 0 , 0 , 0 , 0 ,
: TOKEN-TYPE TOKEN 2 CELLS + @ ;
: TOKEN-VALUE TOKEN 3 CELLS + @ ;
: GETTOK GETINT GETINT TOKEN 2!
GETNAM FIND DROP EXECUTE
DUP Integer = IF GETINT ELSE
DUP String = IF GETSTR INTERN ELSE
DUP Identifier = IF GETNAM INTERN ELSE
0 THEN THEN THEN
TOKEN 3 CELLS + ! TOKEN 2 CELLS + ! ;
: BINARY? TOKEN-TYPE (BINARY?) ;
CREATE PREC #TK @ CELLS ALLOT PREC #TK @ CELLS -1 FILL
: PREC! CELLS PREC + ! ;
14 Op_not PREC! 13 Op_multiply PREC!
13 Op_divide PREC! 13 Op_mod PREC!
12 Op_add PREC! 12 Op_subtract PREC!
10 Op_less PREC! 10 Op_greater PREC!
10 Op_lessequal PREC! 10 Op_greaterequal PREC!
9 Op_equal PREC! 9 Op_notequal PREC!
5 Op_and PREC! 4 Op_or PREC!
: PREC@ CELLS PREC + @ ;
\ Each AST Node is a sequence of cells in data space consisting
\ of the execution token of a printing word, followed by that
\ node's data. Each printing word receives the address of the
\ node's data, and is responsible for printing that data
\ appropriately.
DEFER .NODE
: .NULL DROP ." ;" CR ;
CREATE $NULL ' .NULL ,
: .IDENTIFIER ." Identifier " @ COUNT TYPE CR ;
: $IDENTIFIER ( a-addr --) HERE SWAP ['] .IDENTIFIER , , ;
: .INTEGER ." Integer " @ . CR ;
: $INTEGER ( n --) HERE SWAP ['] .INTEGER , , ;
: "TYPE" [CHAR] " EMIT TYPE [CHAR] " EMIT ;
: .STRING ." String " @ COUNT "TYPE" CR ;
: $STRING ( a-addr --) HERE SWAP ['] .STRING , , ;
: .LEAF DUP @ COUNT TYPE CR CELL+ @ .NODE 0 .NULL ;
: LEAF CREATE HERE CELL+ , BL WORD INTERN .
DOES> HERE >R ['] .LEAF , @ , , R> ;
LEAF $PRTC Prtc LEAF $PRTS Prts LEAF $PRTI Prti
LEAF $NOT Not LEAF $NEGATE Negate
: .BINARY DUP @ COUNT TYPE CR
CELL+ DUP @ .NODE CELL+ @ .NODE ;
: BINARY CREATE HERE CELL+ , BL WORD INTERN .
DOES> HERE >R ['] .BINARY , @ , SWAP 2, R> ;
BINARY $SEQUENCE Sequence BINARY $ASSIGN Assign
BINARY $WHILE While BINARY $IF If
BINARY $SUBTRACT Subtract BINARY $ADD Add
BINARY $MOD Mod BINARY $MULTIPLY Multiply
BINARY $DIVIDE Divide
BINARY $LESS Less BINARY $LESSEQUAL LessEqual
BINARY $GREATER Greater BINARY $GREATEREQUAL GreaterEqual
BINARY $EQUAL Equal BINARY $NOTEQUAL NotEqual
BINARY $AND And BINARY $OR Or
: TOK-CONS ( x* -- node-xt) TOKEN-TYPE CASE
Op_subtract OF ['] $SUBTRACT ENDOF
Op_add OF ['] $ADD ENDOF
op_mod OF ['] $MOD ENDOF
op_multiply OF ['] $MULTIPLY ENDOF
Op_divide OF ['] $DIVIDE ENDOF
Op_equal OF ['] $EQUAL ENDOF
Op_notequal OF ['] $NOTEQUAL ENDOF
Op_less OF ['] $LESS ENDOF
Op_lessequal OF ['] $LESSEQUAL ENDOF
Op_greater OF ['] $GREATER ENDOF
Op_greaterequal OF ['] $GREATEREQUAL ENDOF
Op_and OF ['] $AND ENDOF
Op_or OF ['] $OR ENDOF
ENDCASE ;
: (.NODE) DUP CELL+ SWAP @ EXECUTE ;
' (.NODE) IS .NODE
: .- ( n --) 0 <# #S #> TYPE ;
: EXPECT ( tk --) DUP TOKEN-TYPE <>
IF CR ." stdin:" TOKEN 2@ SWAP .- ." :" .-
." : unexpected token, expecting " . CR BYE
THEN DROP GETTOK ;
: '(' LeftParen EXPECT ;
: ')' RightParen EXPECT ;
: '}' RightBrace EXPECT ;
: ';' Semicolon EXPECT ;
: ',' Comma EXPECT ;
: '=' Op_assign EXPECT ;
DEFER *EXPR DEFER EXPR DEFER STMT
: PAREN-EXPR '(' EXPR ')' ;
: PRIMARY
TOKEN-TYPE LeftParen = IF PAREN-EXPR EXIT THEN
TOKEN-TYPE Op_add = IF GETTOK 12 *EXPR EXIT THEN
TOKEN-TYPE Op_subtract = IF GETTOK 14 *EXPR $NEGATE EXIT THEN
TOKEN-TYPE Op_not = IF GETTOK 14 *EXPR $NOT EXIT THEN
TOKEN-TYPE Identifier = IF TOKEN-VALUE $IDENTIFIER ELSE
TOKEN-TYPE Integer = IF TOKEN-VALUE $INTEGER THEN THEN
GETTOK ;
: (*EXPR) ( n -- node)
PRIMARY ( n node)
BEGIN OVER TOKEN-TYPE PREC@ SWAP OVER <= BINARY? AND
WHILE ( n node prec) 1+ TOK-CONS SWAP GETTOK *EXPR SWAP EXECUTE
REPEAT ( n node prec) DROP NIP ( node) ;
: (EXPR) 0 *EXPR ;
: -)? TOKEN-TYPE RightParen <> ;
: -}? TOKEN-TYPE RightBrace <> ;
: (STMT)
TOKEN-TYPE Semicolon = IF GETTOK STMT EXIT THEN
TOKEN-TYPE Keyword_while =
IF GETTOK PAREN-EXPR STMT $WHILE EXIT THEN
TOKEN-TYPE Keyword_if =
IF GETTOK PAREN-EXPR STMT
TOKEN-TYPE Keyword_else = IF GETTOK STMT ELSE $NULL THEN
$IF $IF EXIT
THEN
TOKEN-TYPE Keyword_putc =
IF GETTOK PAREN-EXPR ';' $PRTC EXIT THEN
TOKEN-TYPE Keyword_print =
IF GETTOK '(' $NULL
BEGIN TOKEN-TYPE String =
IF TOKEN-VALUE $STRING $PRTS GETTOK
ELSE EXPR $PRTI THEN $SEQUENCE -)?
WHILE ',' REPEAT ')' ';' EXIT THEN
TOKEN-TYPE Identifier =
IF TOKEN-VALUE $IDENTIFIER GETTOK '=' EXPR ';' $ASSIGN
EXIT THEN
TOKEN-TYPE LeftBrace =
IF $NULL GETTOK BEGIN -}? WHILE STMT $SEQUENCE REPEAT
'}' EXIT THEN
TOKEN-TYPE End_of_input = IF EXIT THEN EXPR ;
' (*EXPR) IS *EXPR ' (EXPR) IS EXPR ' (STMT) IS STMT
: -EOI? TOKEN-TYPE End_of_input <> ;
: PARSE $NULL GETTOK BEGIN -EOI? WHILE STMT $SEQUENCE REPEAT ;
PARSE .NODE
{{out|case=Count AST}}
Sequence
Sequence
;
Assign
Identifier count
Integer 1
While
Less
Identifier count
Integer 10
Sequence
Sequence
;
Sequence
Sequence
Sequence
;
Prts
String "count is: "
;
Prti
Identifier count
;
Prts
String "\n"
;
Assign
Identifier count
Add
Identifier count
Integer 1
Go
{{trans|C}}
package main
import (
"bufio"
"fmt"
"log"
"os"
"strconv"
"strings"
)
type TokenType int
const (
tkEOI TokenType = iota
tkMul
tkDiv
tkMod
tkAdd
tkSub
tkNegate
tkNot
tkLss
tkLeq
tkGtr
tkGeq
tkEql
tkNeq
tkAssign
tkAnd
tkOr
tkIf
tkElse
tkWhile
tkPrint
tkPutc
tkLparen
tkRparen
tkLbrace
tkRbrace
tkSemi
tkComma
tkIdent
tkInteger
tkString
)
type NodeType int
const (
ndIdent NodeType = iota
ndString
ndInteger
ndSequence
ndIf
ndPrtc
ndPrts
ndPrti
ndWhile
ndAssign
ndNegate
ndNot
ndMul
ndDiv
ndMod
ndAdd
ndSub
ndLss
ndLeq
ndGtr
ndGeq
ndEql
ndNeq
ndAnd
ndOr
)
type tokS struct {
tok TokenType
errLn int
errCol int
text string // ident or string literal or integer value
}
type Tree struct {
nodeType NodeType
left *Tree
right *Tree
value string
}
// dependency: Ordered by tok, must remain in same order as TokenType consts
type atr struct {
text string
enumText string
tok TokenType
rightAssociative bool
isBinary bool
isUnary bool
precedence int
nodeType NodeType
}
var atrs = []atr{
{"EOI", "End_of_input", tkEOI, false, false, false, -1, -1},
{"*", "Op_multiply", tkMul, false, true, false, 13, ndMul},
{"/", "Op_divide", tkDiv, false, true, false, 13, ndDiv},
{"%", "Op_mod", tkMod, false, true, false, 13, ndMod},
{"+", "Op_add", tkAdd, false, true, false, 12, ndAdd},
{"-", "Op_subtract", tkSub, false, true, false, 12, ndSub},
{"-", "Op_negate", tkNegate, false, false, true, 14, ndNegate},
{"!", "Op_not", tkNot, false, false, true, 14, ndNot},
{"<", "Op_less", tkLss, false, true, false, 10, ndLss},
{"<=", "Op_lessequal", tkLeq, false, true, false, 10, ndLeq},
{">", "Op_greater", tkGtr, false, true, false, 10, ndGtr},
{">=", "Op_greaterequal", tkGeq, false, true, false, 10, ndGeq},
{"==", "Op_equal", tkEql, false, true, false, 9, ndEql},
{"!=", "Op_notequal", tkNeq, false, true, false, 9, ndNeq},
{"=", "Op_assign", tkAssign, false, false, false, -1, ndAssign},
{"&&", "Op_and", tkAnd, false, true, false, 5, ndAnd},
{"||", "Op_or", tkOr, false, true, false, 4, ndOr},
{"if", "Keyword_if", tkIf, false, false, false, -1, ndIf},
{"else", "Keyword_else", tkElse, false, false, false, -1, -1},
{"while", "Keyword_while", tkWhile, false, false, false, -1, ndWhile},
{"print", "Keyword_print", tkPrint, false, false, false, -1, -1},
{"putc", "Keyword_putc", tkPutc, false, false, false, -1, -1},
{"(", "LeftParen", tkLparen, false, false, false, -1, -1},
{")", "RightParen", tkRparen, false, false, false, -1, -1},
{"{", "LeftBrace", tkLbrace, false, false, false, -1, -1},
{"}", "RightBrace", tkRbrace, false, false, false, -1, -1},
{";", "Semicolon", tkSemi, false, false, false, -1, -1},
{",", "Comma", tkComma, false, false, false, -1, -1},
{"Ident", "Identifier", tkIdent, false, false, false, -1, ndIdent},
{"Integer literal", "Integer", tkInteger, false, false, false, -1, ndInteger},
{"String literal", "String", tkString, false, false, false, -1, ndString},
}
var displayNodes = []string{
"Identifier", "String", "Integer", "Sequence", "If", "Prtc", "Prts", "Prti",
"While", "Assign", "Negate", "Not", "Multiply", "Divide", "Mod", "Add",
"Subtract", "Less", "LessEqual", "Greater", "GreaterEqual", "Equal",
"NotEqual", "And", "Or",
}
var (
err error
token tokS
scanner *bufio.Scanner
)
func reportError(errLine, errCol int, msg string) {
log.Fatalf("(%d, %d) error : %s\n", errLine, errCol, msg)
}
func check(err error) {
if err != nil {
log.Fatal(err)
}
}
func getEum(name string) TokenType { // return internal version of name#
for _, atr := range atrs {
if atr.enumText == name {
return atr.tok
}
}
reportError(0, 0, fmt.Sprintf("Unknown token %s\n", name))
return tkEOI
}
func getTok() tokS {
tok := tokS{}
if scanner.Scan() {
line := strings.TrimRight(scanner.Text(), " \t")
fields := strings.Fields(line)
// [ ]*{lineno}[ ]+{colno}[ ]+token[ ]+optional
tok.errLn, err = strconv.Atoi(fields[0])
check(err)
tok.errCol, err = strconv.Atoi(fields[1])
check(err)
tok.tok = getEum(fields[2])
le := len(fields)
if le == 4 {
tok.text = fields[3]
} else if le > 4 {
idx := strings.Index(line, `"`)
tok.text = line[idx:]
}
}
check(scanner.Err())
return tok
}
func makeNode(nodeType NodeType, left *Tree, right *Tree) *Tree {
return &Tree{nodeType, left, right, ""}
}
func makeLeaf(nodeType NodeType, value string) *Tree {
return &Tree{nodeType, nil, nil, value}
}
func expect(msg string, s TokenType) {
if token.tok == s {
token = getTok()
return
}
reportError(token.errLn, token.errCol,
fmt.Sprintf("%s: Expecting '%s', found '%s'\n", msg, atrs[s].text, atrs[token.tok].text))
}
func expr(p int) *Tree {
var x, node *Tree
switch token.tok {
case tkLparen:
x = parenExpr()
case tkSub, tkAdd:
op := token.tok
token = getTok()
node = expr(atrs[tkNegate].precedence)
if op == tkSub {
x = makeNode(ndNegate, node, nil)
} else {
x = node
}
case tkNot:
token = getTok()
x = makeNode(ndNot, expr(atrs[tkNot].precedence), nil)
case tkIdent:
x = makeLeaf(ndIdent, token.text)
token = getTok()
case tkInteger:
x = makeLeaf(ndInteger, token.text)
token = getTok()
default:
reportError(token.errLn, token.errCol,
fmt.Sprintf("Expecting a primary, found: %s\n", atrs[token.tok].text))
}
for atrs[token.tok].isBinary && atrs[token.tok].precedence >= p {
op := token.tok
token = getTok()
q := atrs[op].precedence
if !atrs[op].rightAssociative {
q++
}
node = expr(q)
x = makeNode(atrs[op].nodeType, x, node)
}
return x
}
func parenExpr() *Tree {
expect("parenExpr", tkLparen)
t := expr(0)
expect("parenExpr", tkRparen)
return t
}
func stmt() *Tree {
var t, v, e, s, s2 *Tree
switch token.tok {
case tkIf:
token = getTok()
e = parenExpr()
s = stmt()
s2 = nil
if token.tok == tkElse {
token = getTok()
s2 = stmt()
}
t = makeNode(ndIf, e, makeNode(ndIf, s, s2))
case tkPutc:
token = getTok()
e = parenExpr()
t = makeNode(ndPrtc, e, nil)
expect("Putc", tkSemi)
case tkPrint: // print '(' expr {',' expr} ')'
token = getTok()
for expect("Print", tkLparen); ; expect("Print", tkComma) {
if token.tok == tkString {
e = makeNode(ndPrts, makeLeaf(ndString, token.text), nil)
token = getTok()
} else {
e = makeNode(ndPrti, expr(0), nil)
}
t = makeNode(ndSequence, t, e)
if token.tok != tkComma {
break
}
}
expect("Print", tkRparen)
expect("Print", tkSemi)
case tkSemi:
token = getTok()
case tkIdent:
v = makeLeaf(ndIdent, token.text)
token = getTok()
expect("assign", tkAssign)
e = expr(0)
t = makeNode(ndAssign, v, e)
expect("assign", tkSemi)
case tkWhile:
token = getTok()
e = parenExpr()
s = stmt()
t = makeNode(ndWhile, e, s)
case tkLbrace: // {stmt}
for expect("Lbrace", tkLbrace); token.tok != tkRbrace && token.tok != tkEOI; {
t = makeNode(ndSequence, t, stmt())
}
expect("Lbrace", tkRbrace)
case tkEOI:
// do nothing
default:
reportError(token.errLn, token.errCol,
fmt.Sprintf("expecting start of statement, found '%s'\n", atrs[token.tok].text))
}
return t
}
func parse() *Tree {
var t *Tree
token = getTok()
for {
t = makeNode(ndSequence, t, stmt())
if t == nil || token.tok == tkEOI {
break
}
}
return t
}
func prtAst(t *Tree) {
if t == nil {
fmt.Print(";\n")
} else {
fmt.Printf("%-14s ", displayNodes[t.nodeType])
if t.nodeType == ndIdent || t.nodeType == ndInteger || t.nodeType == ndString {
fmt.Printf("%s\n", t.value)
} else {
fmt.Println()
prtAst(t.left)
prtAst(t.right)
}
}
}
func main() {
source, err := os.Open("source.txt")
check(err)
defer source.Close()
scanner = bufio.NewScanner(source)
prtAst(parse())
}
{{out}} Prime Numbers example:
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier count
Integer 1
Assign
Identifier n
Integer 1
Assign
Identifier limit
Integer 100
While
Less
Identifier n
Identifier limit
Sequence
Sequence
Sequence
Sequence
Sequence
;
Assign
Identifier k
Integer 3
Assign
Identifier p
Integer 1
Assign
Identifier n
Add
Identifier n
Integer 2
While
And
LessEqual
Multiply
Identifier k
Identifier k
Identifier n
Identifier p
Sequence
Sequence
;
Assign
Identifier p
NotEqual
Multiply
Divide
Identifier n
Identifier k
Identifier k
Identifier n
Assign
Identifier k
Add
Identifier k
Integer 2
If
Identifier p
If
Sequence
Sequence
;
Sequence
Sequence
;
Prti
Identifier n
;
Prts
String " is prime\n"
;
Assign
Identifier count
Add
Identifier count
Integer 1
;
Sequence
Sequence
Sequence
;
Prts
String "Total primes found: "
;
Prti
Identifier count
;
Prts
String "\n"
;
Java
Usage: java Parser infile [>outfile] {{trans|Python}}
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.StringTokenizer;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.util.HashMap;
class Parser {
private List<Token> source;
private Token token;
private int position;
static class Node {
public NodeType nt;
public Node left, right;
public String value;
Node() {
this.nt = null;
this.left = null;
this.right = null;
this.value = null;
}
Node(NodeType node_type, Node left, Node right, String value) {
this.nt = node_type;
this.left = left;
this.right = right;
this.value = value;
}
public static Node make_node(NodeType nodetype, Node left, Node right) {
return new Node(nodetype, left, right, "");
}
public static Node make_node(NodeType nodetype, Node left) {
return new Node(nodetype, left, null, "");
}
public static Node make_leaf(NodeType nodetype, String value) {
return new Node(nodetype, null, null, value);
}
}
static class Token {
public TokenType tokentype;
public String value;
public int line;
public int pos;
Token(TokenType token, String value, int line, int pos) {
this.tokentype = token; this.value = value; this.line = line; this.pos = pos;
}
@Override
public String toString() {
return String.format("%5d %5d %-15s %s", this.line, this.pos, this.tokentype, this.value);
}
}
static enum TokenType {
End_of_input(false, false, false, -1, NodeType.nd_None),
Op_multiply(false, true, false, 13, NodeType.nd_Mul),
Op_divide(false, true, false, 13, NodeType.nd_Div),
Op_mod(false, true, false, 13, NodeType.nd_Mod),
Op_add(false, true, false, 12, NodeType.nd_Add),
Op_subtract(false, true, false, 12, NodeType.nd_Sub),
Op_negate(false, false, true, 14, NodeType.nd_Negate),
Op_not(false, false, true, 14, NodeType.nd_Not),
Op_less(false, true, false, 10, NodeType.nd_Lss),
Op_lessequal(false, true, false, 10, NodeType.nd_Leq),
Op_greater(false, true, false, 10, NodeType.nd_Gtr),
Op_greaterequal(false, true, false, 10, NodeType.nd_Geq),
Op_equal(false, true, true, 9, NodeType.nd_Eql),
Op_notequal(false, true, false, 9, NodeType.nd_Neq),
Op_assign(false, false, false, -1, NodeType.nd_Assign),
Op_and(false, true, false, 5, NodeType.nd_And),
Op_or(false, true, false, 4, NodeType.nd_Or),
Keyword_if(false, false, false, -1, NodeType.nd_If),
Keyword_else(false, false, false, -1, NodeType.nd_None),
Keyword_while(false, false, false, -1, NodeType.nd_While),
Keyword_print(false, false, false, -1, NodeType.nd_None),
Keyword_putc(false, false, false, -1, NodeType.nd_None),
LeftParen(false, false, false, -1, NodeType.nd_None),
RightParen(false, false, false, -1, NodeType.nd_None),
LeftBrace(false, false, false, -1, NodeType.nd_None),
RightBrace(false, false, false, -1, NodeType.nd_None),
Semicolon(false, false, false, -1, NodeType.nd_None),
Comma(false, false, false, -1, NodeType.nd_None),
Identifier(false, false, false, -1, NodeType.nd_Ident),
Integer(false, false, false, -1, NodeType.nd_Integer),
String(false, false, false, -1, NodeType.nd_String);
private final int precedence;
private final boolean right_assoc;
private final boolean is_binary;
private final boolean is_unary;
private final NodeType node_type;
TokenType(boolean right_assoc, boolean is_binary, boolean is_unary, int precedence, NodeType node) {
this.right_assoc = right_assoc;
this.is_binary = is_binary;
this.is_unary = is_unary;
this.precedence = precedence;
this.node_type = node;
}
boolean isRightAssoc() { return this.right_assoc; }
boolean isBinary() { return this.is_binary; }
boolean isUnary() { return this.is_unary; }
int getPrecedence() { return this.precedence; }
NodeType getNodeType() { return this.node_type; }
}
static enum NodeType {
nd_None(""), nd_Ident("Identifier"), nd_String("String"), nd_Integer("Integer"), nd_Sequence("Sequence"), nd_If("If"),
nd_Prtc("Prtc"), nd_Prts("Prts"), nd_Prti("Prti"), nd_While("While"),
nd_Assign("Assign"), nd_Negate("Negate"), nd_Not("Not"), nd_Mul("Multiply"), nd_Div("Divide"), nd_Mod("Mod"), nd_Add("Add"),
nd_Sub("Subtract"), nd_Lss("Less"), nd_Leq("LessEqual"),
nd_Gtr("Greater"), nd_Geq("GreaterEqual"), nd_Eql("Equal"), nd_Neq("NotEqual"), nd_And("And"), nd_Or("Or");
private final String name;
NodeType(String name) {
this.name = name;
}
@Override
public String toString() { return this.name; }
}
static void error(int line, int pos, String msg) {
if (line > 0 && pos > 0) {
System.out.printf("%s in line %d, pos %d\n", msg, line, pos);
} else {
System.out.println(msg);
}
System.exit(1);
}
Parser(List<Token> source) {
this.source = source;
this.token = null;
this.position = 0;
}
Token getNextToken() {
this.token = this.source.get(this.position++);
return this.token;
}
Node expr(int p) {
Node result = null, node;
TokenType op;
int q;
if (this.token.tokentype == TokenType.LeftParen) {
result = paren_expr();
} else if (this.token.tokentype == TokenType.Op_add || this.token.tokentype == TokenType.Op_subtract) {
op = (this.token.tokentype == TokenType.Op_subtract) ? TokenType.Op_negate : TokenType.Op_add;
getNextToken();
node = expr(TokenType.Op_negate.getPrecedence());
result = (op == TokenType.Op_negate) ? Node.make_node(NodeType.nd_Negate, node) : node;
} else if (this.token.tokentype == TokenType.Op_not) {
getNextToken();
result = Node.make_node(NodeType.nd_Not, expr(TokenType.Op_not.getPrecedence()));
} else if (this.token.tokentype == TokenType.Identifier) {
result = Node.make_leaf(NodeType.nd_Ident, this.token.value);
getNextToken();
} else if (this.token.tokentype == TokenType.Integer) {
result = Node.make_leaf(NodeType.nd_Integer, this.token.value);
getNextToken();
} else {
error(this.token.line, this.token.pos, "Expecting a primary, found: " + this.token.tokentype);
}
while (this.token.tokentype.isBinary() && this.token.tokentype.getPrecedence() >= p) {
op = this.token.tokentype;
getNextToken();
q = op.getPrecedence();
if (!op.isRightAssoc()) {
q++;
}
node = expr(q);
result = Node.make_node(op.getNodeType(), result, node);
}
return result;
}
Node paren_expr() {
expect("paren_expr", TokenType.LeftParen);
Node node = expr(0);
expect("paren_expr", TokenType.RightParen);
return node;
}
void expect(String msg, TokenType s) {
if (this.token.tokentype == s) {
getNextToken();
return;
}
error(this.token.line, this.token.pos, msg + ": Expecting '" + s + "', found: '" + this.token.tokentype + "'");
}
Node stmt() {
Node s, s2, t = null, e, v;
if (this.token.tokentype == TokenType.Keyword_if) {
getNextToken();
e = paren_expr();
s = stmt();
s2 = null;
if (this.token.tokentype == TokenType.Keyword_else) {
getNextToken();
s2 = stmt();
}
t = Node.make_node(NodeType.nd_If, e, Node.make_node(NodeType.nd_If, s, s2));
} else if (this.token.tokentype == TokenType.Keyword_putc) {
getNextToken();
e = paren_expr();
t = Node.make_node(NodeType.nd_Prtc, e);
expect("Putc", TokenType.Semicolon);
} else if (this.token.tokentype == TokenType.Keyword_print) {
getNextToken();
expect("Print", TokenType.LeftParen);
while (true) {
if (this.token.tokentype == TokenType.String) {
e = Node.make_node(NodeType.nd_Prts, Node.make_leaf(NodeType.nd_String, this.token.value));
getNextToken();
} else {
e = Node.make_node(NodeType.nd_Prti, expr(0), null);
}
t = Node.make_node(NodeType.nd_Sequence, t, e);
if (this.token.tokentype != TokenType.Comma) {
break;
}
getNextToken();
}
expect("Print", TokenType.RightParen);
expect("Print", TokenType.Semicolon);
} else if (this.token.tokentype == TokenType.Semicolon) {
getNextToken();
} else if (this.token.tokentype == TokenType.Identifier) {
v = Node.make_leaf(NodeType.nd_Ident, this.token.value);
getNextToken();
expect("assign", TokenType.Op_assign);
e = expr(0);
t = Node.make_node(NodeType.nd_Assign, v, e);
expect("assign", TokenType.Semicolon);
} else if (this.token.tokentype == TokenType.Keyword_while) {
getNextToken();
e = paren_expr();
s = stmt();
t = Node.make_node(NodeType.nd_While, e, s);
} else if (this.token.tokentype == TokenType.LeftBrace) {
getNextToken();
while (this.token.tokentype != TokenType.RightBrace && this.token.tokentype != TokenType.End_of_input) {
t = Node.make_node(NodeType.nd_Sequence, t, stmt());
}
expect("LBrace", TokenType.RightBrace);
} else if (this.token.tokentype == TokenType.End_of_input) {
} else {
error(this.token.line, this.token.pos, "Expecting start of statement, found: " + this.token.tokentype);
}
return t;
}
Node parse() {
Node t = null;
getNextToken();
while (this.token.tokentype != TokenType.End_of_input) {
t = Node.make_node(NodeType.nd_Sequence, t, stmt());
}
return t;
}
void printAST(Node t) {
int i = 0;
if (t == null) {
System.out.println(";");
} else {
System.out.printf("%-14s", t.nt);
if (t.nt == NodeType.nd_Ident || t.nt == NodeType.nd_Integer || t.nt == NodeType.nd_String) {
System.out.println(" " + t.value);
} else {
System.out.println();
printAST(t.left);
printAST(t.right);
}
}
}
public static void main(String[] args) {
if (args.length > 0) {
try {
String value, token;
int line, pos;
Token t;
boolean found;
List<Token> list = new ArrayList<>();
Map<String, TokenType> str_to_tokens = new HashMap<>();
str_to_tokens.put("End_of_input", TokenType.End_of_input);
str_to_tokens.put("Op_multiply", TokenType.Op_multiply);
str_to_tokens.put("Op_divide", TokenType.Op_divide);
str_to_tokens.put("Op_mod", TokenType.Op_mod);
str_to_tokens.put("Op_add", TokenType.Op_add);
str_to_tokens.put("Op_subtract", TokenType.Op_subtract);
str_to_tokens.put("Op_negate", TokenType.Op_negate);
str_to_tokens.put("Op_not", TokenType.Op_not);
str_to_tokens.put("Op_less", TokenType.Op_less);
str_to_tokens.put("Op_lessequal", TokenType.Op_lessequal);
str_to_tokens.put("Op_greater", TokenType.Op_greater);
str_to_tokens.put("Op_greaterequal", TokenType.Op_greaterequal);
str_to_tokens.put("Op_equal", TokenType.Op_equal);
str_to_tokens.put("Op_notequal", TokenType.Op_notequal);
str_to_tokens.put("Op_assign", TokenType.Op_assign);
str_to_tokens.put("Op_and", TokenType.Op_and);
str_to_tokens.put("Op_or", TokenType.Op_or);
str_to_tokens.put("Keyword_if", TokenType.Keyword_if);
str_to_tokens.put("Keyword_else", TokenType.Keyword_else);
str_to_tokens.put("Keyword_while", TokenType.Keyword_while);
str_to_tokens.put("Keyword_print", TokenType.Keyword_print);
str_to_tokens.put("Keyword_putc", TokenType.Keyword_putc);
str_to_tokens.put("LeftParen", TokenType.LeftParen);
str_to_tokens.put("RightParen", TokenType.RightParen);
str_to_tokens.put("LeftBrace", TokenType.LeftBrace);
str_to_tokens.put("RightBrace", TokenType.RightBrace);
str_to_tokens.put("Semicolon", TokenType.Semicolon);
str_to_tokens.put("Comma", TokenType.Comma);
str_to_tokens.put("Identifier", TokenType.Identifier);
str_to_tokens.put("Integer", TokenType.Integer);
str_to_tokens.put("String", TokenType.String);
Scanner s = new Scanner(new File(args[0]));
String source = " ";
while (s.hasNext()) {
String str = s.nextLine();
StringTokenizer st = new StringTokenizer(str);
line = Integer.parseInt(st.nextToken());
pos = Integer.parseInt(st.nextToken());
token = st.nextToken();
value = "";
while (st.hasMoreTokens()) {
value += st.nextToken() + " ";
}
found = false;
if (str_to_tokens.containsKey(token)) {
found = true;
list.add(new Token(str_to_tokens.get(token), value, line, pos));
}
if (found == false) {
throw new Exception("Token not found: '" + token + "'");
}
}
Parser p = new Parser(list);
p.printAST(p.parse());
} catch (FileNotFoundException e) {
error(-1, -1, "Exception: " + e.getMessage());
} catch (Exception e) {
error(-1, -1, "Exception: " + e.getMessage());
}
} else {
error(-1, -1, "No args");
}
}
}
Julia
Julia tends to discourage large numbers of global variables, so this direct port from the Python reference implementation moves the globals into a function wrapper. {{trans|Python}}
struct ASTnode
nodetype::Int
left::Union{Nothing, ASTnode}
right::Union{Nothing, ASTnode}
value::Union{Nothing, Int, String}
end
function syntaxanalyzer(inputfile)
tkEOI, tkMul, tkDiv, tkMod, tkAdd, tkSub, tkNegate, tkNot, tkLss, tkLeq, tkGtr, tkGeq,
tkEql, tkNeq, tkAssign, tkAnd, tkOr, tkIf, tkElse, tkWhile, tkPrint, tkPutc, tkLparen, tkRparen,
tkLbrace, tkRbrace, tkSemi, tkComma, tkIdent, tkInteger, tkString = collect(1:31)
ndIdent, ndString, ndInteger, ndSequence, ndIf, ndPrtc, ndPrts, ndPrti, ndWhile,
ndAssign, ndNegate, ndNot, ndMul, ndDiv, ndMod, ndAdd, ndSub, ndLss, ndLeq,
ndGtr, ndGeq, ndEql, ndNeq, ndAnd, ndOr = collect(1:25)
TK_NAME, TK_RIGHT_ASSOC, TK_IS_BINARY, TK_IS_UNARY, TK_PRECEDENCE, TK_NODE = collect(1:6) # label Token columns
Tokens = [
["EOI" , false, false, false, -1, -1 ],
["*" , false, true, false, 13, ndMul ],
["/" , false, true, false, 13, ndDiv ],
["%" , false, true, false, 13, ndMod ],
["+" , false, true, false, 12, ndAdd ],
["-" , false, true, false, 12, ndSub ],
["-" , false, false, true, 14, ndNegate ],
["!" , false, false, true, 14, ndNot ],
["<" , false, true, false, 10, ndLss ],
["<=" , false, true, false, 10, ndLeq ],
[">" , false, true, false, 10, ndGtr ],
[">=" , false, true, false, 10, ndGeq ],
["==" , false, true, false, 9, ndEql ],
["!=" , false, true, false, 9, ndNeq ],
["=" , false, false, false, -1, ndAssign ],
["&&" , false, true, false, 5, ndAnd ],
["||" , false, true, false, 4, ndOr ],
["if" , false, false, false, -1, ndIf ],
["else" , false, false, false, -1, -1 ],
["while" , false, false, false, -1, ndWhile ],
["print" , false, false, false, -1, -1 ],
["putc" , false, false, false, -1, -1 ],
["(" , false, false, false, -1, -1 ],
[")" , false, false, false, -1, -1 ],
["{" , false, false, false, -1, -1 ],
["}" , false, false, false, -1, -1 ],
[";" , false, false, false, -1, -1 ],
["," , false, false, false, -1, -1 ],
["Ident" , false, false, false, -1, ndIdent ],
["Integer literal" , false, false, false, -1, ndInteger],
["String literal" , false, false, false, -1, ndString ]]
allsyms = Dict(
"End_of_input" => tkEOI, "Op_multiply" => tkMul, "Op_divide" => tkDiv,
"Op_mod" => tkMod, "Op_add" => tkAdd, "Op_subtract" => tkSub,
"Op_negate" => tkNegate, "Op_not" => tkNot, "Op_less" => tkLss,
"Op_lessequal" => tkLeq, "Op_greater" => tkGtr, "Op_greaterequal" => tkGeq,
"Op_equal" => tkEql, "Op_notequal" => tkNeq, "Op_assign" => tkAssign,
"Op_and" => tkAnd, "Op_or" => tkOr, "Keyword_if" => tkIf, "Keyword_else" => tkElse,
"Keyword_while" => tkWhile, "Keyword_print" => tkPrint, "Keyword_putc" => tkPutc,
"LeftParen" => tkLparen, "RightParen" => tkRparen, "LeftBrace" => tkLbrace,
"RightBrace" => tkRbrace, "Semicolon" => tkSemi, "Comma" => tkComma,
"Identifier" => tkIdent, "Integer" => tkInteger, "String" => tkString)
displaynodes = ["Identifier", "String", "Integer", "Sequence", "If", "Prtc", "Prts", "Prti", "While",
"Assign", "Negate", "Not", "Multiply", "Divide", "Mod", "Add", "Subtract", "Less",
"LessEqual", "Greater", "GreaterEqual", "Equal", "NotEqual", "And", "Or"]
errline, errcol, tok, toktext = fill("", 4)
error(msg) = throw("Error in syntax: $msg.")
nilnode = ASTnode(0, nothing, nothing, nothing)
tokother = ""
function gettok()
s = readline(inputfile)
if length(s) == 0
error("empty line")
end
linelist = split(strip(s), r"\s+", limit = 4)
# line col Ident varname
# 0 1 2 3
errline, errcol, toktext = linelist[1:3]
if !haskey(allsyms, toktext)
error("Unknown token $toktext")
end
tok = allsyms[toktext]
tokother = (tok in [tkInteger, tkIdent, tkString]) ? linelist[4] : ""
end
makenode(oper, left, right = nilnode) = ASTnode(oper, left, right, nothing)
makeleaf(oper, n::Int) = ASTnode(oper, nothing, nothing, n)
makeleaf(oper, n) = ASTnode(oper, nothing, nothing, string(n))
expect(msg, s) = if tok != s error("msg: Expecting $(Tokens[s][TK_NAME]), found $(Tokens[tok][TK_NAME])") else gettok() end
function expr(p)
x = nilnode
if tok == tkLparen
x = parenexpr()
elseif tok in [tkSub, tkAdd]
op = tok == tkSub ? tkNegate : tkAdd
gettok()
node = expr(Tokens[tkNegate][TK_PRECEDENCE])
x = (op == tkNegate) ? makenode(ndNegate, node) : node
elseif tok == tkNot
gettok()
x = makenode(ndNot, expr(Tokens[tkNot][TK_PRECEDENCE]))
elseif tok == tkIdent
x = makeleaf(ndIdent, tokother)
gettok()
elseif tok == tkInteger
x = makeleaf(ndInteger, tokother)
gettok()
else
error("Expecting a primary, found: $(Tokens[tok][TK_NAME])")
end
while Tokens[tok][TK_IS_BINARY] && (Tokens[tok][TK_PRECEDENCE] >= p)
op = tok
gettok()
q = Tokens[op][TK_PRECEDENCE]
if !Tokens[op][TK_RIGHT_ASSOC]
q += 1
end
node = expr(q)
x = makenode(Tokens[op][TK_NODE], x, node)
end
x
end
parenexpr() = (expect("paren_expr", tkLparen); node = expr(0); expect("paren_expr", tkRparen); node)
function stmt()
t = nilnode
if tok == tkIf
gettok()
e = parenexpr()
s = stmt()
s2 = nilnode
if tok == tkElse
gettok()
s2 = stmt()
end
t = makenode(ndIf, e, makenode(ndIf, s, s2))
elseif tok == tkPutc
gettok()
e = parenexpr()
t = makenode(ndPrtc, e)
expect("Putc", tkSemi)
elseif tok == tkPrint
gettok()
expect("Print", tkLparen)
while true
if tok == tkString
e = makenode(ndPrts, makeleaf(ndString, tokother))
gettok()
else
e = makenode(ndPrti, expr(0))
end
t = makenode(ndSequence, t, e)
if tok != tkComma
break
end
gettok()
end
expect("Print", tkRparen)
expect("Print", tkSemi)
elseif tok == tkSemi
gettok()
elseif tok == tkIdent
v = makeleaf(ndIdent, tokother)
gettok()
expect("assign", tkAssign)
e = expr(0)
t = makenode(ndAssign, v, e)
expect("assign", tkSemi)
elseif tok == tkWhile
gettok()
e = parenexpr()
s = stmt()
t = makenode(ndWhile, e, s)
elseif tok == tkLbrace
gettok()
while (tok != tkRbrace) && (tok != tkEOI)
t = makenode(ndSequence, t, stmt())
end
expect("Lbrace", tkRbrace)
elseif tok != tkEOI
error("Expecting start of statement, found: $(Tokens[tok][TK_NAME])")
end
return t
end
function parse()
t = nilnode
gettok()
while true
t = makenode(ndSequence, t, stmt())
if (tok == tkEOI) || (t == nilnode)
break
end
end
t
end
function prtASTnode(t)
if t == nothing
return
elseif t == nilnode
println(";")
elseif t.nodetype in [ndIdent, ndInteger, ndString]
println(rpad(displaynodes[t.nodetype], 14), t.value)
else
println(rpad(displaynodes[t.nodetype], 14))
end
prtASTnode(t.left)
prtASTnode(t.right)
end
# runs the function
prtASTnode(parse())
end
testtxt = """
1 1 Identifier count
1 7 Op_assign
1 9 Integer 1
1 10 Semicolon
2 1 Keyword_while
2 7 LeftParen
2 8 Identifier count
2 14 Op_less
2 16 Integer 10
2 18 RightParen
2 20 LeftBrace
3 5 Keyword_print
3 10 LeftParen
3 11 String \"count is: \"
3 23 Comma
3 25 Identifier count
3 30 Comma
3 32 String \"\\n\"
3 36 RightParen
3 37 Semicolon
4 5 Identifier count
4 11 Op_assign
4 13 Identifier count
4 19 Op_add
4 21 Integer 1
4 22 Semicolon
5 1 RightBrace
6 1 End_of_input """
syntaxanalyzer(IOBuffer(testtxt)) # for isolated testing
# syntaxanalyzer(length(ARGS) > 1 ? ARGS[1] : stdin) # for use as in the Python code
M2000 Interpreter
This program written without functions. Subs use the current stack of values (a feature from interpreter) to return arrays. Subs run on same scope as the module or function which called. We use Local to make local variables (erased at return). Sub prt_ast() called first time without passing parameter, because parameter already exist in stack of values. Interpreter when call a module, a function, a subroutine always pass values to stack of values. Functions called in an expression, always have own stack of values. Modules call other modules passing the same stack of values. Threads are parts of modules, with same scope in module where belong, but have own stack and static variables, and they rub in time intervals.
A (1,2,3) is an auto array or tuple. We can assign a tuple in a variable, in a item in another tuple. A tuple is a reference type, but here we don't use a second pointer (we say references variables which references to other variables - reference or value type-, so we say pointer the reference who hold an object alive. We can read 2nd item (expected string) from alfa, a pointer to array, using array$(alfa,1) or alfa#val$(1). The second variation can be used multiple times if a tuple has another tulple so alfa#val(2)#val$(1) return a string from 3rd item, which expect a tuple from 2nd item. The other variation array$(array(alfa,2),1) for the same result.
Module syntax_analyzer(b$){
enum tokens {
Op_add, Op_subtract, Op_not=5, Op_multiply=10, Op_divide, Op_mod,
Op_negate, Op_less, Op_lessequal, Op_greater, Op_greaterequal,
Op_equal, Op_notequal, Op_and, Op_or, Op_assign=100, Keyword_if=110,
Keyword_else, Keyword_while, Keyword_print, Keyword_putc, LeftParen, RightParen,
LeftBrace, RightBrace, Semicolon, Comma, Identifier, Integer, String, End_of_input
}
Inventory precedence=Op_multiply:=13, Op_divide:=13, Op_mod:=13, Op_add:=12, Op_subtract:=12
Append precedence, Op_negate:=14, Op_not:=14, Op_less:=10, Op_lessequal:=10, Op_greater:=10
Append precedence, Op_greaterequal:=10, Op_equal:=9, Op_notequal:=9, Op_assign:=-1, Op_and:=5
Append precedence, Op_or:=4
Inventory symbols=Op_multiply:="Multiply", Op_divide:="Divide", Op_mod:="Mod", Op_add:="Add"
Append symbols, Op_negate:="Negate", Op_not:="Not", Op_less:="Less", Op_subtract:="Subtract"
Append symbols, Op_lessequal:="LessEqual", Op_greater:="Greater", Op_greaterequal:="GreaterEqual"
Append symbols, Op_equal:="Equal", Op_notequal:="NotEqual", Op_and:="And", Op_or:="Or"
def lineNo, ColumnNo, m, line$, a, lim, cur=-1
const nl$=chr$(13)+chr$(10), Ansi=3
Dim lex$()
lex$()=piece$(b$,chr$(13)+chr$(10))
lim=dimension(lex$(),1)-1
op=End_of_input
flush
k=0
Try {
push (,) ' Null
getone(&op)
repeat
stmt(&op)
shift 2 ' swap two top items
push ("Sequence", array, array)
k++
until op=End_of_Input
}
er$=error$
if er$<>"" then print er$ : flush: break
Print "Ast"
Document Output$
prt_ast()
clipboard Output$
Save.Doc Output$, "parse.t", Ansi
document parse$
Load.Doc parse$,"parse.t", Ansi
Report parse$
sub prt_ast(t)
if len(t)<1 then
Output$=";"+nl$
else.if len(t)=3 then
Output$=t#val$(0) +nl$
prt_ast(t#val(1)) : prt_ast(t#val(2))
else
Output$=t#val$(0) +nl$
end if
end sub
sub expr(p) ' only a number
local x=(,), prev=op
if op>=Identifier then
x=(line$,)
getone(&op)
else.if op=LeftParen then
paren_exp()
x=array
else.if op<10 then
getone(&op)
expr(precedence(int(Op_negate)))
read local y
if prev=Op_add then
x=y
else
if prev=Op_subtract then prev=Op_negate
x=(symbols(prev), y,(,))
End if
else
{error "??? "+eval$(op)}
end if
local prec
while exist(precedence, int(op))
prev=op : prec=eval(precedence)
if prec<14 and prec>=p else exit
getone(&op)
expr(prec+1) ' all operators are left associative (use prec for right a.)
x=(symbols(int(prev)), x, array)
End While
Push x
end sub
sub paren_exp()
expected(LeftParen)
getone(&op)
expr(0)
expected(RightParen)
getone(&op)
end sub
sub stmt(&op)
local t=(,)
if op=Identifier then
t=(line$)
getone(&op)
expected(Op_assign)
getone(&op)
expr(0)
read local rightnode
Push ("Assign",t,rightnode)
expected(Semicolon)
getone(&op)
else.if op=Semicolon then
getone(&op)
Push (";",)
else.if op=Keyword_print then
getone(&op)
expected(LeftParen)
repeat
getone(&op)
if op=String then
Push ("Prts",(line$,),(,))
getone(&op)
else
expr(0)
Push ("Prti", array,(,))
end if
t=("Sequence", t, array)
until op<>Comma
expected(RightParen)
getone(&op)
expected(Semicolon)
getone(&op)
push t
else.if op=Keyword_while then
getone(&op)
paren_exp()
stmt(&op)
shift 2
Push ("While",array, array)
else.if op=Keyword_if then
getone(&op)
paren_exp()
stmt(&op)
local s2=(,)
if op=Keyword_else then
getone(&op)
stmt(&op)
read s2
end if
shift 2
Push ("If",array ,("If",array,s2))
else.if op=Keyword_putc then
getone(&op)
paren_exp()
Push ("Prtc",array,t)
expected(Semicolon)
getone(&op)
else.if op=LeftBrace then
Brace()
else
error "Unkown Op"
end if
end sub
Sub Brace()
getone(&op)
while op<>RightBrace and op<>End_of_input
stmt(&op)
t=("Sequence", t, array)
end while
expected(RightBrace)
getone(&op)
push t
End Sub
Sub expected(what)
if not op=what then {Error "Expected "+eval$(what)+str$(LineNo)+","+Str$(ColumnNo)}
End Sub
sub getone(&op)
op=End_of_input
while cur<lim
cur++
line$=trim$(lex$(cur))
if line$<>"" then exit
end while
if cur=lim then exit sub
LineNo=Val(line$,"int",m)
line$=mid$(line$, m)
ColumnNo=Val(line$,"int",m)
line$=trim$(mid$(line$, m))
Rem : Print LineNo, ColumnNo
m=instr(line$," ")
if m>0 then op=Eval("."+leftpart$(line$, " ")) else op=Eval("."+line$)
end sub
}
syntax_analyzer {
1 1 LeftBrace
5 5 Identifier left_edge
5 17 Op_assign
5 19 Op_subtract
5 20 Integer 420
5 23 Semicolon
6 5 Identifier right_edge
6 17 Op_assign
6 20 Integer 300
6 23 Semicolon
7 5 Identifier top_edge
7 17 Op_assign
7 20 Integer 300
7 23 Semicolon
8 5 Identifier bottom_edge
8 17 Op_assign
8 19 Op_subtract
8 20 Integer 300
8 23 Semicolon
9 5 Identifier x_step
9 17 Op_assign
9 22 Integer 7
9 23 Semicolon
10 5 Identifier y_step
10 17 Op_assign
10 21 Integer 15
10 23 Semicolon
12 5 Identifier max_iter
12 17 Op_assign
12 20 Integer 200
12 23 Semicolon
14 5 Identifier y0
14 8 Op_assign
14 10 Identifier top_edge
14 18 Semicolon
15 5 Keyword_while
15 11 LeftParen
15 12 Identifier y0
15 15 Op_greater
15 17 Identifier bottom_edge
15 28 RightParen
15 30 LeftBrace
16 9 Identifier x0
16 12 Op_assign
16 14 Identifier left_edge
16 23 Semicolon
17 9 Keyword_while
17 15 LeftParen
17 16 Identifier x0
17 19 Op_less
17 21 Identifier right_edge
17 31 RightParen
17 33 LeftBrace
18 13 Identifier y
18 15 Op_assign
18 17 Integer 0
18 18 Semicolon
19 13 Identifier x
19 15 Op_assign
19 17 Integer 0
19 18 Semicolon
20 13 Identifier the_char
20 22 Op_assign
20 24 Integer 32
20 27 Semicolon
21 13 Identifier i
21 15 Op_assign
21 17 Integer 0
21 18 Semicolon
22 13 Keyword_while
22 19 LeftParen
22 20 Identifier i
22 22 Op_less
22 24 Identifier max_iter
22 32 RightParen
22 34 LeftBrace
23 17 Identifier x_x
23 21 Op_assign
23 23 LeftParen
23 24 Identifier x
23 26 Op_multiply
23 28 Identifier x
23 29 RightParen
23 31 Op_divide
23 33 Integer 200
23 36 Semicolon
24 17 Identifier y_y
24 21 Op_assign
24 23 LeftParen
24 24 Identifier y
24 26 Op_multiply
24 28 Identifier y
24 29 RightParen
24 31 Op_divide
24 33 Integer 200
24 36 Semicolon
25 17 Keyword_if
25 20 LeftParen
25 21 Identifier x_x
25 25 Op_add
25 27 Identifier y_y
25 31 Op_greater
25 33 Integer 800
25 37 RightParen
25 39 LeftBrace
26 21 Identifier the_char
26 30 Op_assign
26 32 Integer 48
26 36 Op_add
26 38 Identifier i
26 39 Semicolon
27 21 Keyword_if
27 24 LeftParen
27 25 Identifier i
27 27 Op_greater
27 29 Integer 9
27 30 RightParen
27 32 LeftBrace
28 25 Identifier the_char
28 34 Op_assign
28 36 Integer 64
28 39 Semicolon
29 21 RightBrace
30 21 Identifier i
30 23 Op_assign
30 25 Identifier max_iter
30 33 Semicolon
31 17 RightBrace
32 17 Identifier y
32 19 Op_assign
32 21 Identifier x
32 23 Op_multiply
32 25 Identifier y
32 27 Op_divide
32 29 Integer 100
32 33 Op_add
32 35 Identifier y0
32 37 Semicolon
33 17 Identifier x
33 19 Op_assign
33 21 Identifier x_x
33 25 Op_subtract
33 27 Identifier y_y
33 31 Op_add
33 33 Identifier x0
33 35 Semicolon
34 17 Identifier i
34 19 Op_assign
34 21 Identifier i
34 23 Op_add
34 25 Integer 1
34 26 Semicolon
35 13 RightBrace
36 13 Keyword_putc
36 17 LeftParen
36 18 Identifier the_char
36 26 RightParen
36 27 Semicolon
37 13 Identifier x0
37 16 Op_assign
37 18 Identifier x0
37 21 Op_add
37 23 Identifier x_step
37 29 Semicolon
38 9 RightBrace
39 9 Keyword_putc
39 13 LeftParen
39 14 Integer 10
39 18 RightParen
39 19 Semicolon
40 9 Identifier y0
40 12 Op_assign
40 14 Identifier y0
40 17 Op_subtract
40 19 Identifier y_step
40 25 Semicolon
41 5 RightBrace
42 1 RightBrace
43 1 End_of_Input
}
{{out}}
Sequence ; Sequence Sequence Sequence Sequence Sequence Sequence Sequence Sequence Sequence ; Assign Identifier left_edge Negate Integer 420 ; Assign Identifier right_edge Integer 300 Assign Identifier top_edge Integer 300 Assign Identifier bottom_edge Negate Integer 300 ; Assign Identifier x_step Integer 7 Assign Identifier y_step Integer 15 Assign Identifier max_iter Integer 200 Assign Identifier y0 Identifier top_edge While Greater Identifier y0 Identifier bottom_edge Sequence Sequence Sequence Sequence ; Assign Identifier x0 Identifier left_edge While Less Identifier x0 Identifier right_edge Sequence Sequence Sequence Sequence Sequence Sequence Sequence ; Assign Identifier y Integer 0 Assign Identifier x Integer 0 Assign Identifier the_char Integer 32 Assign Identifier i Integer 0 While Less Identifier i Identifier max_iter Sequence Sequence Sequence Sequence Sequence Sequence ; Assign Identifier x_x Divide Multiply Identifier x Identifier x Integer 200 Assign Identifier y_y Divide Multiply Identifier y Identifier y Integer 200 If Greater Add Identifier x_x Identifier y_y Integer 800 if Sequence Sequence Sequence ; Assign Identifier the_char Add Integer 48 Identifier i If Greater Identifier i Integer 9 if Sequence ; Assign Identifier the_char Integer 64 ; Assign Identifier i Identifier max_iter ; Assign Identifier y Add Divide Multiply Identifier x Identifier y Integer 100 Identifier y0 Assign Identifier x Add Subtract Identifier x_x Identifier y_y Identifier x0 Assign Identifier i Add Identifier i Integer 1 Putc Identifier the_char ; Assign Identifier x0 Add Identifier x0 Identifier x_step Putc Integer 10 ; Assign Identifier y0 Subtract Identifier y0 Identifier y_step## Perl Tested on perl v5.26.1 ```Perl #!/usr/bin/perl use strict; # parse.pl - inputs lex, outputs flattened ast use warnings; # http://www.rosettacode.org/wiki/Compiler/syntax_analyzer my $h = qr/\G\s*\d+\s+\d+\s+/; # header of each line sub error { die "*** Expected @_ at " . (/\G(.*\n)/ ? $1 =~ s/^\s*(\d+)\s+(\d+)\s+/line $1 character $2 got /r : "EOF\n") } sub want { /$h \Q$_[1]\E.*\n/gcx ? shift : error "'$_[1]'" } local $_ = join '', <>; print want stmtlist(), 'End_of_input'; sub stmtlist { /(?=$h (RightBrace|End_of_input))/gcx and return ";\n"; my ($stmt, $stmtlist) = (stmt(), stmtlist()); $stmtlist eq ";\n" ? $stmt : "Sequence\n$stmt$stmtlist"; } sub stmt { /$h Semicolon\n/gcx ? ";\n" : /$h Identifier \s+ (\w+) \n/gcx ? want("Assign\nIdentifier\t$1\n", 'Op_assign') . want expr(0), 'Semicolon' : /$h Keyword_while \n/gcx ? "While\n" . parenexp() . stmt() : /$h Keyword_if \n/gcx ? "If\n" . parenexp() . "If\n" . stmt() . (/$h Keyword_else \n/gcx ? stmt() : ";\n") : /$h Keyword_print \n/gcx ? want('', 'LeftParen') . want want(printlist(), 'RightParen'), 'Semicolon' : /$h Keyword_putc \n/gcx ? want "Prtc\n" . parenexp() . ";\n", 'Semicolon' : /$h LeftBrace \n/gcx ? want stmtlist(), 'RightBrace' : error 'A STMT'; } sub parenexp { want('', 'LeftParen') . want expr(0), 'RightParen' } # (expr) sub printlist { my $ast = /$h String \s+ (".*") \n/gcx ? "Prts\nString\t\t$1\n;\n" : "Prti\n" . expr(0) . ";\n"; /$h Comma \n/gcx ? "Sequence\n$ast" . printlist() : $ast; } sub expr # (sort of EBNF) expr = operand { operator expr } { my $ast = # operand /$h Integer \s+ (\d+) \n/gcx ? "Integer\t\t$1\n" : /$h Identifier \s+ (\w+) \n/gcx ? "Identifier\t$1\n" : /$h LeftParen \n/gcx ? want expr(0), 'RightParen' : /$h Op_(negate|subtract) \n/gcx ? "Negate\n" . expr(8) . ";\n" : /$h Op_not \n/gcx ? "Not\n" . expr(8) . ";\n" : /$h Op_add \n/gcx ? expr(8) : error "A PRIMARY"; $ast = # { operator expr } $_[0] <= 7 && /$h Op_multiply \n/gcx ? "Multiply\n$ast" . expr(8) : $_[0] <= 7 && /$h Op_divide \n/gcx ? "Divide\n$ast" . expr(8) : $_[0] <= 7 && /$h Op_mod \n/gcx ? "Mod\n$ast" . expr(8) : $_[0] <= 6 && /$h Op_add \n/gcx ? "Add\n$ast" . expr(7) : $_[0] <= 6 && /$h Op_subtract \n/gcx ? "Subtract\n$ast" . expr(7) : $_[0] == 5 && /(?=$h Op_(less|greater)(equal)? \n)/gcx ? error 'NO ASSOC' : $_[0] <= 5 && /$h Op_lessequal \n/gcx ? "LessEqual\n$ast" . expr(5) : $_[0] <= 5 && /$h Op_less \n/gcx ? "Less\n$ast" . expr(5) : $_[0] <= 5 && /$h Op_greater \n/gcx ? "Greater\n$ast" . expr(5) : $_[0] <= 5 && /$h Op_greaterequal \n/gcx ? "GreaterEqual\n$ast" . expr(5) : $_[0] == 3 && /(?=$h Op_(not)?equal \n)/gcx ? error 'NO ASSOC' : $_[0] <= 3 && /$h Op_equal \n/gcx ? "Equal\n$ast" . expr(3) : $_[0] <= 3 && /$h Op_notequal \n/gcx ? "NotEqual\n$ast" . expr(3) : $_[0] <= 1 && /$h Op_and \n/gcx ? "And\n$ast" . expr(2) : $_[0] <= 0 && /$h Op_or \n/gcx ? "Or\n$ast" . expr(1) : return $ast while 1; } ``` {{out|case=Count AST}} ```txt Sequence Assign Identifier count Integer 1 While Less Identifier count Integer 10 Sequence Sequence Prts String "count is: " ; Sequence Prti Identifier count ; Prts String "\n" ; Assign Identifier count Add Identifier count Integer 1 ``` ## Phix Reusing lex.e (and core.e) from the [[Compiler/lexical_analyzer#Phix|Lexical Analyzer task]], and again written as a reusable module. ```Phix -- -- demo\\rosetta\\Compiler\\parse.e -- ### ========================== -- -- The reusable part of parse.exw -- include lex.e sequence tok procedure errd(sequence msg, sequence args={}) {tok_line,tok_col} = tok error(msg,args) end procedure global sequence toks integer next_tok = 1 function get_tok() sequence tok = toks[next_tok] next_tok += 1 return tok end function procedure expect(string msg, integer s) integer tk = tok[3] if tk!=s then errd("%s: Expecting '%s', found '%s'\n", {msg, tkNames[s], tkNames[tk]}) end if tok = get_tok() end procedure function expr(integer p) object x = NULL, node integer op = tok[3] switch op do case tk_LeftParen: tok = get_tok() x = expr(0) expect("expr",tk_RightParen) case tk_sub: case tk_add: tok = get_tok() node = expr(precedences[tk_neg]); x = iff(op==tk_sub?{tk_neg, node, NULL}:node) case tk_not: tok = get_tok(); x = {tk_not, expr(precedences[tk_not]), NULL} case tk_Identifier: x = {tk_Identifier, tok[4]} tok = get_tok(); case tk_Integer: x = {tk_Integer, tok[4]} tok = get_tok(); default: errd("Expecting a primary, found: %s\n", tkNames[op]) end switch op = tok[3] while narys[op]=BINARY and precedences[op]>=p do tok = get_tok() x = {op, x, expr(precedences[op]+1)} op = tok[3] end while return x; end function function paren_expr(string msg) expect(msg, tk_LeftParen); object t = expr(0) expect(msg, tk_RightParen); return t end function function stmt() object t = NULL, e, s switch tok[3] do case tk_if: tok = get_tok(); object condition = paren_expr("If-cond"); object ifblock = stmt(); object elseblock = NULL; if tok[3] == tk_else then tok = get_tok(); elseblock = stmt(); end if t = {tk_if, condition, {tk_if, ifblock, elseblock}} case tk_putc: tok = get_tok(); e = paren_expr("Prtc") t = {tk_putc, e, NULL} expect("Putc", tk_Semicolon); case tk_print: tok = get_tok(); expect("Print",tk_LeftParen) while 1 do if tok[3] == tk_String then e = {tk_Prints, {tk_String, tok[4]}, NULL} tok = get_tok(); else e = {tk_Printi, expr(0), NULL} end if t = {tk_Sequence, t, e} if tok[3]!=tk_Comma then exit end if expect("Print", tk_Comma) end while expect("Print", tk_RightParen); expect("Print", tk_Semicolon); case tk_Semicolon: tok = get_tok(); case tk_Identifier: object v v = {tk_Identifier, tok[4]} tok = get_tok(); expect("assign", tk_assign); e = expr(0); t = {tk_assign, v, e} expect("assign", tk_Semicolon); case tk_while: tok = get_tok(); e = paren_expr("while"); s = stmt(); t = {tk_while, e, s} case tk_LeftBrace: /* {stmt} */ expect("LeftBrace", tk_LeftBrace) while not find(tok[3],{tk_RightBrace,tk_EOI}) do t = {tk_Sequence, t, stmt()} end while expect("LeftBrace", tk_RightBrace); break; case tk_EOI: break; default: errd("expecting start of statement, found '%s'\n", tkNames[tok[3]]); end switch return t end function global function parse() object t = NULL tok = get_tok() while 1 do object s = stmt() if s=NULL then exit end if t = {tk_Sequence, t, s} end while return t end function ``` And a simple test driver for the specific task: ```Phix -- -- demo\\rosetta\\Compiler\\parse.exw -- ### ============================ -- include parse.e procedure print_ast(object t) if t == NULL then printf(output_file,";\n") else integer ttype = t[1] printf(output_file,tkNames[ttype]) if ttype=tk_Identifier then printf(output_file," %s\n",t[2]) elsif ttype=tk_Integer then printf(output_file," %d\n",t[2]) elsif ttype=tk_String then printf(output_file," %s\n",enquote(t[2])) else printf(output_file,"\n") print_ast(t[2]) print_ast(t[3]) end if end if end procedure procedure main(sequence cl) open_files(cl) toks = lex() object t = parse() print_ast(t) close_files() end procedure --main(command_line()) main({0,0,"test3.c"}) -- not parseable! --main({0,0,"primes.c"}) -- as Algol, C, Python (apart from spacing) --main({0,0,"count.c"}) -- as AWK ( "" ) ``` {{out}} ```txt Line 5 column 40: Print: Expecting 'LeftParen', found 'Op_subtract' ``` ## Python Tested with Python 2.7 and 3.x ```Python from __future__ import print_function import sys, shlex, operator tk_EOI, tk_Mul, tk_Div, tk_Mod, tk_Add, tk_Sub, tk_Negate, tk_Not, tk_Lss, tk_Leq, tk_Gtr, \ tk_Geq, tk_Eql, tk_Neq, tk_Assign, tk_And, tk_Or, tk_If, tk_Else, tk_While, tk_Print, \ tk_Putc, tk_Lparen, tk_Rparen, tk_Lbrace, tk_Rbrace, tk_Semi, tk_Comma, tk_Ident, \ tk_Integer, tk_String = range(31) nd_Ident, nd_String, nd_Integer, nd_Sequence, nd_If, nd_Prtc, nd_Prts, nd_Prti, nd_While, \ nd_Assign, nd_Negate, nd_Not, nd_Mul, nd_Div, nd_Mod, nd_Add, nd_Sub, nd_Lss, nd_Leq, \ nd_Gtr, nd_Geq, nd_Eql, nd_Neq, nd_And, nd_Or = range(25) # must have same order as above Tokens = [ ["EOI" , False, False, False, -1, -1 ], ["*" , False, True, False, 13, nd_Mul ], ["/" , False, True, False, 13, nd_Div ], ["%" , False, True, False, 13, nd_Mod ], ["+" , False, True, False, 12, nd_Add ], ["-" , False, True, False, 12, nd_Sub ], ["-" , False, False, True, 14, nd_Negate ], ["!" , False, False, True, 14, nd_Not ], ["<" , False, True, False, 10, nd_Lss ], ["<=" , False, True, False, 10, nd_Leq ], [">" , False, True, False, 10, nd_Gtr ], [">=" , False, True, False, 10, nd_Geq ], ["==" , False, True, False, 9, nd_Eql ], ["!=" , False, True, False, 9, nd_Neq ], ["=" , False, False, False, -1, nd_Assign ], ["&&" , False, True, False, 5, nd_And ], ["||" , False, True, False, 4, nd_Or ], ["if" , False, False, False, -1, nd_If ], ["else" , False, False, False, -1, -1 ], ["while" , False, False, False, -1, nd_While ], ["print" , False, False, False, -1, -1 ], ["putc" , False, False, False, -1, -1 ], ["(" , False, False, False, -1, -1 ], [")" , False, False, False, -1, -1 ], ["{" , False, False, False, -1, -1 ], ["}" , False, False, False, -1, -1 ], [";" , False, False, False, -1, -1 ], ["," , False, False, False, -1, -1 ], ["Ident" , False, False, False, -1, nd_Ident ], ["Integer literal" , False, False, False, -1, nd_Integer], ["String literal" , False, False, False, -1, nd_String ] ] all_syms = {"End_of_input" : tk_EOI, "Op_multiply" : tk_Mul, "Op_divide" : tk_Div, "Op_mod" : tk_Mod, "Op_add" : tk_Add, "Op_subtract" : tk_Sub, "Op_negate" : tk_Negate, "Op_not" : tk_Not, "Op_less" : tk_Lss, "Op_lessequal" : tk_Leq, "Op_greater" : tk_Gtr, "Op_greaterequal": tk_Geq, "Op_equal" : tk_Eql, "Op_notequal" : tk_Neq, "Op_assign" : tk_Assign, "Op_and" : tk_And, "Op_or" : tk_Or, "Keyword_if" : tk_If, "Keyword_else" : tk_Else, "Keyword_while" : tk_While, "Keyword_print" : tk_Print, "Keyword_putc" : tk_Putc, "LeftParen" : tk_Lparen, "RightParen" : tk_Rparen, "LeftBrace" : tk_Lbrace, "RightBrace" : tk_Rbrace, "Semicolon" : tk_Semi, "Comma" : tk_Comma, "Identifier" : tk_Ident, "Integer" : tk_Integer, "String" : tk_String} Display_nodes = ["Identifier", "String", "Integer", "Sequence", "If", "Prtc", "Prts", "Prti", "While", "Assign", "Negate", "Not", "Multiply", "Divide", "Mod", "Add", "Subtract", "Less", "LessEqual", "Greater", "GreaterEqual", "Equal", "NotEqual", "And", "Or"] TK_NAME = 0 TK_RIGHT_ASSOC = 1 TK_IS_BINARY = 2 TK_IS_UNARY = 3 TK_PRECEDENCE = 4 TK_NODE = 5 input_file = None err_line = None err_col = None tok = None tok_text = None #*** show error and exit def error(msg): print("(%d, %d) %s" % (int(err_line), int(err_col), msg)) exit(1) #*** def gettok(): global err_line, err_col, tok, tok_text, tok_other line = input_file.readline() if len(line) == 0: error("empty line") line_list = shlex.split(line, False, False) # line col Ident var_name # 0 1 2 3 err_line = line_list[0] err_col = line_list[1] tok_text = line_list[2] tok = all_syms.get(tok_text) if tok == None: error("Unknown token %s" % (tok_text)) tok_other = None if tok in [tk_Integer, tk_Ident, tk_String]: tok_other = line_list[3] class Node: def __init__(self, node_type, left = None, right = None, value = None): self.node_type = node_type self.left = left self.right = right self.value = value #*** def make_node(oper, left, right = None): return Node(oper, left, right) #*** def make_leaf(oper, n): return Node(oper, value = n) #*** def expect(msg, s): if tok == s: gettok() return error("%s: Expecting '%s', found '%s'" % (msg, Tokens[s][TK_NAME], Tokens[tok][TK_NAME])) #*** def expr(p): x = None if tok == tk_Lparen: x = paren_expr() elif tok in [tk_Sub, tk_Add]: op = (tk_Negate if tok == tk_Sub else tk_Add) gettok() node = expr(Tokens[tk_Negate][TK_PRECEDENCE]) x = (make_node(nd_Negate, node) if op == tk_Negate else node) elif tok == tk_Not: gettok() x = make_node(nd_Not, expr(Tokens[tk_Not][TK_PRECEDENCE])) elif tok == tk_Ident: x = make_leaf(nd_Ident, tok_other) gettok() elif tok == tk_Integer: x = make_leaf(nd_Integer, tok_other) gettok() else: error("Expecting a primary, found: %s" % (Tokens[tok][TK_NAME])) while Tokens[tok][TK_IS_BINARY] and Tokens[tok][TK_PRECEDENCE] >= p: op = tok gettok() q = Tokens[op][TK_PRECEDENCE] if not Tokens[op][TK_RIGHT_ASSOC]: q += 1 node = expr(q) x = make_node(Tokens[op][TK_NODE], x, node) return x #*** def paren_expr(): expect("paren_expr", tk_Lparen) node = expr(0) expect("paren_expr", tk_Rparen) return node #*** def stmt(): t = None if tok == tk_If: gettok() e = paren_expr() s = stmt() s2 = None if tok == tk_Else: gettok() s2 = stmt() t = make_node(nd_If, e, make_node(nd_If, s, s2)) elif tok == tk_Putc: gettok() e = paren_expr() t = make_node(nd_Prtc, e) expect("Putc", tk_Semi) elif tok == tk_Print: gettok() expect("Print", tk_Lparen) while True: if tok == tk_String: e = make_node(nd_Prts, make_leaf(nd_String, tok_other)) gettok() else: e = make_node(nd_Prti, expr(0)) t = make_node(nd_Sequence, t, e) if tok != tk_Comma: break gettok() expect("Print", tk_Rparen) expect("Print", tk_Semi) elif tok == tk_Semi: gettok() elif tok == tk_Ident: v = make_leaf(nd_Ident, tok_other) gettok() expect("assign", tk_Assign) e = expr(0) t = make_node(nd_Assign, v, e) expect("assign", tk_Semi) elif tok == tk_While: gettok() e = paren_expr() s = stmt() t = make_node(nd_While, e, s) elif tok == tk_Lbrace: gettok() while tok != tk_Rbrace and tok != tk_EOI: t = make_node(nd_Sequence, t, stmt()) expect("Lbrace", tk_Rbrace) elif tok == tk_EOI: pass else: error("Expecting start of statement, found: %s" % (Tokens[tok][TK_NAME])) return t #*** def parse(): t = None gettok() while True: t = make_node(nd_Sequence, t, stmt()) if tok == tk_EOI or t == None: break return t def prt_ast(t): if t == None: print(";") else: print("%-14s" % (Display_nodes[t.node_type]), end='') if t.node_type in [nd_Ident, nd_Integer]: print("%s" % (t.value)) elif t.node_type == nd_String: print("%s" %(t.value)) else: print("") prt_ast(t.left) prt_ast(t.right) #*** main driver input_file = sys.stdin if len(sys.argv) > 1: try: input_file = open(sys.argv[1], "r", 4096) except IOError as e: error(0, 0, "Can't open %s" % sys.argv[1]) t = parse() prt_ast(t) ``` {{out|case=prime numbers AST}} ```txt Sequence Sequence Sequence Sequence Sequence ; Assign Identifier count Integer 1 Assign Identifier n Integer 1 Assign Identifier limit Integer 100 While Less Identifier n Identifier limit Sequence Sequence Sequence Sequence Sequence ; Assign Identifier k Integer 3 Assign Identifier p Integer 1 Assign Identifier n Add Identifier n Integer 2 While And LessEqual Multiply Identifier k Identifier k Identifier n Identifier p Sequence Sequence ; Assign Identifier p NotEqual Multiply Divide Identifier n Identifier k Identifier k Identifier n Assign Identifier k Add Identifier k Integer 2 If Identifier p If Sequence Sequence ; Sequence Sequence ; Prti Identifier n ; Prts String " is prime\n" ; Assign Identifier count Add Identifier count Integer 1 ; Sequence Sequence Sequence ; Prts String "Total primes found: " ; Prti Identifier count ; Prts String "\n" ; ``` ## Scheme Code implements a recursive descent parser based on the given grammar. Tested against all programs in [[Compiler/Sample programs]]. ```scheme (import (scheme base) (scheme process-context) (scheme write)) (define *names* (list (cons 'Op_add 'Add) (cons 'Op_subtract 'Subtract) (cons 'Op_multiply 'Multiply) (cons 'Op_divide 'Divide) (cons 'Op_mod 'Mod) (cons 'Op_not 'Not) (cons 'Op_equal 'Equal) (cons 'Op_notequal 'NotEqual) (cons 'Op_or 'Or) (cons 'Op_and 'And) (cons 'Op_less 'Less) (cons 'Op_lessequal 'LessEqual) (cons 'Op_greater 'Greater) (cons 'Op_greaterequal 'GreaterEqual))) (define (retrieve-name type) (let ((res (assq type *names*))) (if res (cdr res) (error "Unknown type name")))) ;; takes a vector of tokens (define (parse tokens) ; read statements, until hit end of tokens (define posn 0) (define (peek-token) (vector-ref tokens posn)) (define (get-token) (set! posn (+ 1 posn)) (vector-ref tokens (- posn 1))) (define (match type) (if (eq? (car (vector-ref tokens posn)) type) (set! posn (+ 1 posn)) (error "Could not match token type" type))) ; make it easier to read token parts (define type car) (define value cadr) ; ;; left associative read of one or more items with given separators (define (read-one-or-more reader separators) (let loop ((lft (reader))) (let ((next (peek-token))) (if (memq (type next) separators) (begin (match (type next)) (loop (list (retrieve-name (type next)) lft (reader)))) lft)))) ; ;; read one or two items with given separator (define (read-one-or-two reader separators) (let* ((lft (reader)) (next (peek-token))) (if (memq (type next) separators) (begin (match (type next)) (list (retrieve-name (type next)) lft (reader))) lft))) ; (define (read-primary) (let ((next (get-token))) (case (type next) ((Identifier Integer) next) ((LeftParen) (let ((v (read-expr))) (match 'RightParen) v)) ((Op_add) ; + sign is ignored (read-primary)) ((Op_not) (list 'Not (read-primary) '())) ((Op_subtract) (list 'Negate (read-primary) '())) (else (error "Unknown primary type"))))) ; (define (read-multiplication-expr) ; * (read-one-or-more read-primary '(Op_multiply Op_divide Op_mod))) ; (define (read-addition-expr) ; * (read-one-or-more read-multiplication-expr '(Op_add Op_subtract))) ; (define (read-relational-expr) ; ? (read-one-or-two read-addition-expr '(Op_less Op_lessequal Op_greater Op_greaterequal))) ; (define (read-equality-expr) ; ? (read-one-or-two read-relational-expr '(Op_equal Op_notequal))) ; (define (read-and-expr) ; * (read-one-or-more read-equality-expr '(Op_and))) ; (define (read-expr) ; * (read-one-or-more read-and-expr '(Op_or))) ; (define (read-prt-list) (define (read-print-part) (if (eq? (type (peek-token)) 'String) (list 'Prts (get-token) '()) (list 'Prti (read-expr) '()))) ; (do ((tok (read-print-part) (read-print-part)) (rec '() (list 'Sequence rec tok))) ((not (eq? (type (peek-token)) 'Comma)) (list 'Sequence rec tok)) (match 'Comma))) ; (define (read-paren-expr) (match 'LeftParen) (let ((v (read-expr))) (match 'RightParen) v)) ; (define (read-stmt) (case (type (peek-token)) ((SemiColon) '()) ((Identifier) (let ((id (get-token))) (match 'Op_assign) (let ((ex (read-expr))) (match 'Semicolon) (list 'Assign id ex)))) ((Keyword_while) (match 'Keyword_while) (let* ((expr (read-paren-expr)) (stmt (read-stmt))) (list 'While expr stmt))) ((Keyword_if) (match 'Keyword_if) (let* ((expr (read-paren-expr)) (then-part (read-stmt)) (else-part (if (eq? (type (peek-token)) 'Keyword_else) (begin (match 'Keyword_else) (read-stmt)) '()))) (list 'If expr (list 'If then-part else-part)))) ((Keyword_print) (match 'Keyword_print) (match 'LeftParen) (let ((v (read-prt-list))) (match 'RightParen) (match 'Semicolon) v)) ((Keyword_putc) (match 'Keyword_putc) (let ((v (read-paren-expr))) (match 'Semicolon) (list 'Putc v '()))) ((LeftBrace) (match 'LeftBrace) (let ((v (read-stmts))) (match 'RightBrace) v)) (else (error "Unknown token type for statement" (type (peek-token)))))) ; (define (read-stmts) (do ((sequence (list 'Sequence '() (read-stmt)) (list 'Sequence sequence (read-stmt)))) ((memq (type (peek-token)) '(End_of_input RightBrace)) sequence))) ; (let ((res (read-stmts))) (match 'End_of_input) res)) ;; reads tokens from file, parses and returns the AST (define (parse-file filename) (define (tokenise line) (let ((port (open-input-string line))) (read port) ; discard line (read port) ; discard col (let* ((type (read port)) ; read type as symbol (val (read port))) ; check for optional value (if (eof-object? val) (list type) (list type val))))) ; (with-input-from-file filename (lambda () (do ((line (read-line) (read-line)) (toks '() (cons (tokenise line) toks))) ((eof-object? line) (parse (list->vector (reverse toks)))))))) ;; Output the AST in flattened format (define (display-ast ast) (cond ((null? ast) (display ";\n")) ((= 2 (length ast)) (display (car ast)) (display #\tab) (write (cadr ast)) ; use write to preserve " " on String (newline)) (else (display (car ast)) (newline) (display-ast (cadr ast)) (display-ast (cadr (cdr ast)))))) ;; read from filename passed on command line (if (= 2 (length (command-line))) (display-ast (parse-file (cadr (command-line)))) (display "Error: provide program filename\n")) ```