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{{task|Programming language concepts}} {{Control Structures}}
Assume functions a and b return boolean values, and further, the execution of function b takes considerable resources without side effects, and is to be minimized.
If we needed to compute the conjunction (and):
:::: x = a() and b()
Then it would be best to not compute the value of b() if the value of a() is computed as false, as the value of x can then only ever be false.
Similarly, if we needed to compute the disjunction (or):
:::: y = a() or b()
Then it would be best to not compute the value of b() if the value of a() is computed as true, as the value of y can then only ever be true.
Some languages will stop further computation of boolean equations as soon as the result is known, so-called [[wp:Short-circuit evaluation|short-circuit evaluation]] of boolean expressions
;Task:
Create two functions named a and b, that take and return the same boolean value.
The functions should also print their name whenever they are called.
Calculate and assign the values of the following equations to a variable in such a way that function b is only called when necessary:
:::: x = a(i) and b(j)
:::: y = a(i) or b(j)
If the language does not have short-circuit evaluation, this might be achieved with nested '''if''' statements.
Ada
Ada has built-in short-circuit operations '''and then''' and '''or else''':
with Ada.Text_IO; use Ada.Text_IO;
procedure Test_Short_Circuit is
function A (Value : Boolean) return Boolean is
begin
Put (" A=" & Boolean'Image (Value));
return Value;
end A;
function B (Value : Boolean) return Boolean is
begin
Put (" B=" & Boolean'Image (Value));
return Value;
end B;
begin
for I in Boolean'Range loop
for J in Boolean'Range loop
Put (" (A and then B)=" & Boolean'Image (A (I) and then B (J)));
New_Line;
end loop;
end loop;
for I in Boolean'Range loop
for J in Boolean'Range loop
Put (" (A or else B)=" & Boolean'Image (A (I) or else B (J)));
New_Line;
end loop;
end loop;
end Test_Short_Circuit;
{{out|Sample output}}
A=FALSE (A and then B)=FALSE
A=FALSE (A and then B)=FALSE
A=TRUE B=FALSE (A and then B)=FALSE
A=TRUE B=TRUE (A and then B)=TRUE
A=FALSE B=FALSE (A or else B)=FALSE
A=FALSE B=TRUE (A or else B)=TRUE
A=TRUE (A or else B)=TRUE
A=TRUE (A or else B)=TRUE
ALGOL 68
With Standard
{{works with|ALGOL 68|Revision 1 - no extensions to language used}} {{works with|ALGOL 68G|Any - tested with release [http://sourceforge.net/projects/algol68/files/algol68g/algol68g-1.18.0/algol68g-1.18.0-9h.tiny.el5.centos.fc11.i386.rpm/download 1.18.0-9h.tiny]}} {{works with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d]}} Note: The "brief" ''conditional clause'' ( ~ | ~ | ~ ) is a the standard's ''shorthand'' for enforcing ''short-circuit evaluation''. Moreover, the coder is able to define their own '''proc'''[edures] and '''op'''[erators] that implement ''short-circuit evaluation'' by using Algol68's ''proceduring''.
PRIO ORELSE = 2, ANDTHEN = 3; # user defined operators #
OP ORELSE = (BOOL a, PROC BOOL b)BOOL: ( a | a | b ),
ANDTHEN = (BOOL a, PROC BOOL b)BOOL: ( a | b | a );
# user defined Short-circuit_evaluation procedures #
PROC or else = (BOOL a, PROC BOOL b)BOOL: ( a | a | b ),
and then = (BOOL a, PROC BOOL b)BOOL: ( a | b | a );
test:(
PROC a = (BOOL a)BOOL: ( print(("a=",a,", ")); a),
b = (BOOL b)BOOL: ( print(("b=",b,", ")); b);
CO
# Valid for Algol 68 Rev0: using "user defined" operators #
# Note: here BOOL is being automatically "procedured" to PROC BOOL #
print(("T ORELSE F = ", a(TRUE) ORELSE b(FALSE), new line));
print(("F ANDTHEN T = ", a(FALSE) ANDTHEN b(TRUE), new line));
print(("or else(T, F) = ", or else(a(TRUE), b(FALSE)), new line));
print(("and then(F, T) = ", and then(a(FALSE), b(TRUE)), new line));
END CO
# Valid for Algol68 Rev1: using "user defined" operators #
# Note: BOOL must be manually "procedured" to PROC BOOL #
print(("T ORELSE F = ", a(TRUE) ORELSE (BOOL:b(FALSE)), new line));
print(("T ORELSE T = ", a(TRUE) ORELSE (BOOL:b(TRUE)), new line));
print(("F ANDTHEN F = ", a(FALSE) ANDTHEN (BOOL:b(FALSE)), new line));
print(("F ANDTHEN T = ", a(FALSE) ANDTHEN (BOOL:b(TRUE)), new line));
print(("F ORELSE F = ", a(FALSE) ORELSE (BOOL:b(FALSE)), new line));
print(("F ORELSE T = ", a(FALSE) ORELSE (BOOL:b(TRUE)), new line));
print(("T ANDTHEN F = ", a(TRUE) ANDTHEN (BOOL:b(FALSE)), new line));
print(("T ANDTHEN T = ", a(TRUE) ANDTHEN (BOOL:b(TRUE)), new line))
)
{{out}}
a=T, T ORELSE F = T
a=T, T ORELSE T = T
a=F, F ANDTHEN F = F
a=F, F ANDTHEN T = F
a=F, b=F, F ORELSE F = F
a=F, b=T, F ORELSE T = T
a=T, b=F, T ANDTHEN F = F
a=T, b=T, T ANDTHEN T = T
With Extensions
{{works with|ALGOL 68G|Any - tested with release [http://sourceforge.net/projects/algol68/files/algol68g/algol68g-1.18.0/algol68g-1.18.0-9h.tiny.el5.centos.fc11.i386.rpm/download 1.18.0-9h.tiny]}} {{works with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d]}}
test:(
PROC a = (BOOL a)BOOL: ( print(("a=",a,", ")); a),
b = (BOOL b)BOOL: ( print(("b=",b,", ")); b);
# Valid for Algol 68G and 68RS using non standard operators #
print(("T OREL F = ", a(TRUE) OREL b(FALSE), new line));
print(("T OREL T = ", a(TRUE) OREL b(TRUE), new line));
print(("F ANDTH F = ", a(FALSE) ANDTH b(FALSE), new line));
print(("F ANDTH T = ", a(FALSE) ANDTH b(TRUE), new line));
print(("F OREL F = ", a(FALSE) OREL b(FALSE), new line));
print(("F OREL T = ", a(FALSE) OREL b(TRUE), new line));
print(("T ANDTH F = ", a(TRUE) ANDTH b(FALSE), new line));
print(("T ANDTH T = ", a(TRUE) ANDTH b(TRUE), new line))
CO;
# Valid for Algol 68G and 68C using non standard operators #
print(("T ORF F = ", a(TRUE) ORF b(FALSE), new line));
print(("F ANDF T = ", a(FALSE) ANDF b(TRUE), new line))
END CO
)
{{out}}
a=T, T OREL F = T
a=T, T OREL T = T
a=F, F ANDTH F = F
a=F, F ANDTH T = F
a=F, b=F, F OREL F = F
a=F, b=T, F OREL T = T
a=T, b=F, T ANDTH F = F
a=T, b=T, T ANDTH T = T
ALGOL W
In Algol W the boolean "and" and "or" operators are short circuit operators.
begin
logical procedure a( logical value v ) ; begin write( "a: ", v ); v end ;
logical procedure b( logical value v ) ; begin write( "b: ", v ); v end ;
write( "and: ", a( true ) and b( true ) );
write( "---" );
write( "or: ", a( true ) or b( true ) );
write( "---" );
write( "and: ", a( false ) and b( true ) );
write( "---" );
write( "or: ", a( false ) or b( true ) );
write( "---" );
end.
{{out}}
and:
a: true
b: true true
---
or:
a: true true
---
and:
a: false false
---
or:
a: false
b: true true
---
AppleScript
AppleScript's boolean operators are short-circuiting (as can be seen from the log below).
What AppleScript lacks, however, is a short-circuiting ternary operator like the '''e ? e2 : e3''' of C, or a short-circuiting three-argument function like '''cond''' in Lisp. To get a similar effect in AppleScript, we have to delay evaluation on both sides, using a '''cond''' which returns a reference to one of two unapplied handlers, and composing the result with a separate '''apply''' function, to apply the selected handler function to its argument.
(As a statement, rather than an expression, the ''if ... then ... else'' structure does not compose – unlike ''cond'' or ''? :'', it can not be nested inside expressions)
on run
map(test, {|and|, |or|})
end run
-- test :: ((Bool, Bool) -> Bool) -> (Bool, Bool, Bool, Bool)
on test(f)
map(f, {{true, true}, {true, false}, {false, true}, {false, false}})
end test
-- |and| :: (Bool, Bool) -> Bool
on |and|(tuple)
set {x, y} to tuple
a(x) and b(y)
end |and|
-- |or| :: (Bool, Bool) -> Bool
on |or|(tuple)
set {x, y} to tuple
a(x) or b(y)
end |or|
-- a :: Bool -> Bool
on a(bool)
log "a"
return bool
end a
-- b :: Bool -> Bool
on b(bool)
log "b"
return bool
end b
-- map :: (a -> b) -> [a] -> [b]
on map(f, xs)
script mf
property lambda : f
end script
set lng to length of xs
set lst to {}
repeat with i from 1 to lng
set end of lst to mf's lambda(item i of xs, i, xs)
end repeat
return lst
end map
{{Out}}
Messages:
(*a*)
(*b*)
(*a*)
(*b*)
(*a*)
(*a*)
(*a*)
(*a*)
(*a*)
(*b*)
(*a*)
(*b*)
Result:
{{true, false, false, false}, {true, true, true, false}}
AutoHotkey
In AutoHotkey, the boolean operators, '''and''', '''or''', and ternaries, short-circuit:
i = 1
j = 1
x := a(i) and b(j)
y := a(i) or b(j)
a(p)
{
MsgBox, a() was called with the parameter "%p%".
Return, p
}
b(p)
{
MsgBox, b() was called with the parameter "%p%".
Return, p
}
AWK
Short-circuit evalation is done in logical AND (&&) and logical OR (||) operators:
#!/usr/bin/awk -f
BEGIN {
print (a(1) && b(1))
print (a(1) || b(1))
print (a(0) && b(1))
print (a(0) || b(1))
}
function a(x) {
print " x:"x
return x
}
function b(y) {
print " y:"y
return y
}
{{out}}
x:1
y:1
1
x:1
1
x:0
0
x:0
y:1
1
Axe
TEST(0,0)
TEST(0,1)
TEST(1,0)
TEST(1,1)
Return
Lbl TEST
r₁→X
r₂→Y
Disp X▶Hex+3," and ",Y▶Hex+3," = ",(A(X)?B(Y))▶Hex+3,i
Disp X▶Hex+3," or ",Y▶Hex+3," = ",(A(X)??B(Y))▶Hex+3,i
.Wait for keypress
getKeyʳ
Return
Lbl A
r₁
Return
Lbl B
r₁
Return
BaCon
BaCon supports short-circuit evaluation.
' Short-circuit evaluation
FUNCTION a(f)
PRINT "FUNCTION a"
RETURN f
END FUNCTION
FUNCTION b(f)
PRINT "FUNCTION b"
RETURN f
END FUNCTION
PRINT "FALSE and TRUE"
x = a(FALSE) AND b(TRUE)
PRINT x
PRINT "TRUE and TRUE"
x = a(TRUE) AND b(TRUE)
PRINT x
PRINT "FALSE or FALSE"
y = a(FALSE) OR b(FALSE)
PRINT y
PRINT "TRUE or FALSE"
y = a(TRUE) OR b(FALSE)
PRINT y
{{out}}
prompt$ ./short-circuit
FALSE and TRUE
FUNCTION a
0
TRUE and TRUE
FUNCTION a
FUNCTION b
1
FALSE or FALSE
FUNCTION a
FUNCTION b
0
TRUE or FALSE
FUNCTION a
1
Batch File
{{trans|Liberty BASIC}}
%
### Batch Files have no booleans.
%
%
### I will instead use 1 as true and 0 as false.
%
@echo off
setlocal enabledelayedexpansion
echo AND
for /l %%i in (0,1,1) do (
for /l %%j in (0,1,1) do (
echo.a^(%%i^) AND b^(%%j^)
call :a %%i
set res=!bool_a!
if not !res!==0 (
call :b %%j
set res=!bool_b!
)
echo.=^> !res!
)
)
echo ---------------------------------
echo OR
for /l %%i in (0,1,1) do (
for /l %%j in (0,1,1) do (
echo a^(%%i^) OR b^(%%j^)
call :a %%i
set res=!bool_a!
if !res!==0 (
call :b %%j
set res=!bool_b!
)
echo.=^> !res!
)
)
pause>nul
exit /b 0
::----------------------------------------
:a
echo. calls func a
set bool_a=%1
goto :EOF
:b
echo. calls func b
set bool_b=%1
goto :EOF
{{Out}}
AND
a(0) AND b(0)
calls func a
=> 0
a(0) AND b(1)
calls func a
=> 0
a(1) AND b(0)
calls func a
calls func b
=> 0
a(1) AND b(1)
calls func a
calls func b
=> 1
---------------------------------
OR
a(0) OR b(0)
calls func a
calls func b
=> 0
a(0) OR b(1)
calls func a
calls func b
=> 1
a(1) OR b(0)
calls func a
=> 1
a(1) OR b(1)
calls func a
=> 1
BBC BASIC
Short-circuit operators aren't implemented directly, but short-circuit AND can be simulated using cascaded IFs. Short-circuit OR can be converted into a short-circuit AND using De Morgan's laws.
REM TRUE is represented as -1, FALSE as 0
FOR i% = TRUE TO FALSE
FOR j% = TRUE TO FALSE
PRINT "For x=a(";FNboolstring(i%);") AND b(";FNboolstring(j%);")"
x% = FALSE
REM Short-circuit AND can be simulated by cascaded IFs:
IF FNa(i%) IF FNb(j%) THEN x%=TRUE
PRINT "x is ";FNboolstring(x%)
PRINT
PRINT "For y=a(";FNboolstring(i%);") OR b(";FNboolstring(j%);")"
y% = FALSE
REM Short-circuit OR can be simulated by De Morgan's laws:
IF NOTFNa(i%) IF NOTFNb(j%) ELSE y%=TRUE : REM Note ELSE without THEN
PRINT "y is ";FNboolstring(y%)
PRINT
NEXT:NEXT
END
DEFFNa(bool%)
PRINT "Function A used; ";
=bool%
DEFFNb(bool%)
PRINT "Function B used; ";
=bool%
DEFFNboolstring(bool%)
IF bool%=0 THEN ="FALSE" ELSE="TRUE"
This gives the results shown below:
For x=a(TRUE) AND b(TRUE)
Function A used; Function B used; x is TRUE
For y=a(TRUE) OR b(TRUE)
Function A used; y is TRUE
For x=a(TRUE) AND b(FALSE)
Function A used; Function B used; x is FALSE
For y=a(TRUE) OR b(FALSE)
Function A used; y is TRUE
For x=a(FALSE) AND b(TRUE)
Function A used; x is FALSE
For y=a(FALSE) OR b(TRUE)
Function A used; Function B used; y is TRUE
For x=a(FALSE) AND b(FALSE)
Function A used; x is FALSE
For y=a(FALSE) OR b(FALSE)
Function A used; Function B used; y is FALSE
Bracmat
Bracmat has no booleans. The closest thing is the success or failure of an expression. A function is not called if the argument fails, so we have to use a trick to pass 'failure' to a function. Here it is accomplished by an extra level of indirection: two == in the definition of 'false' (and 'true', for symmetry) and two !! when evaluating the argument in the functions a and b. The backtick is another hack. This prefix tells Bracmat to look the other way if the backticked expression fails and to continue as if the expression succeeded. A neater way is to introduce an extra OR operator. That solution would have obscured the core of the current task. Short-circuit evaluation is heavily used in Bracmat code. Although not required, it is a good habit to exclusively use AND (&) and OR (|) operators to separate expressions, as the code below exemplifies.
( (a=.out$"I'm a"&!!arg)
& (b=.out$"I'm b"&!!arg)
& (false==~)
& (true==)
& !false !true:?outer
& whl
' ( !outer:%?x ?outer
& !false !true:?inner
& whl
' ( !inner:%?y ?inner
& out
$ ( Testing
(!!x&true|false)
AND
(!!y&true|false)
)
& `(a$!x&b$!y)
& out
$ ( Testing
(!!x&true|false)
OR
(!!y&true|false)
)
& `(a$!x|b$!y)
)
)
& done
);
Output:
Testing false AND false
I'm a
Testing false OR false
I'm a
I'm b
Testing false AND true
I'm a
Testing false OR true
I'm a
I'm b
Testing true AND false
I'm a
I'm b
Testing true OR false
I'm a
Testing true AND true
I'm a
I'm b
Testing true OR true
I'm a
C
Boolean operators
#include <stdio.h>
#include <stdbool.h>
bool a(bool in)
{
printf("I am a\n");
return in;
}
bool b(bool in)
{
printf("I am b\n");
return in;
}
#define TEST(X,Y,O) \
do { \
x = a(X) O b(Y); \
printf(#X " " #O " " #Y " = %s\n\n", x ? "true" : "false"); \
} while(false);
int main()
{
bool x;
TEST(false, true, &&); // b is not evaluated
TEST(true, false, ||); // b is not evaluated
TEST(true, false, &&); // b is evaluated
TEST(false, false, ||); // b is evaluated
return 0;
}
C++
Just like C, boolean operators
#include <iostream>
bool a(bool in)
{
std::cout << "a" << std::endl;
return in;
}
bool b(bool in)
{
std::cout << "b" << std::endl;
return in;
}
void test(bool i, bool j) {
std::cout << std::boolalpha << i << " and " << j << " = " << (a(i) && b(j)) << std::endl;
std::cout << std::boolalpha << i << " or " << j << " = " << (a(i) || b(j)) << std::endl;
}
int main()
{
test(false, false);
test(false, true);
test(true, false);
test(true, true);
return 0;
}
{{out}}
a
false and false = false
a
b
false or false = false
a
false and true = false
a
b
false or true = true
a
b
true and false = false
a
true or false = true
a
b
true and true = true
a
true or true = true
C#
using System;
class Program
{
static bool a(bool value)
{
Console.WriteLine("a");
return value;
}
static bool b(bool value)
{
Console.WriteLine("b");
return value;
}
static void Main()
{
foreach (var i in new[] { false, true })
{
foreach (var j in new[] { false, true })
{
Console.WriteLine("{0} and {1} = {2}", i, j, a(i) && b(j));
Console.WriteLine();
Console.WriteLine("{0} or {1} = {2}", i, j, a(i) || b(j));
Console.WriteLine();
}
}
}
}
{{out}}
a b False or False = False
a False and True = False
a b False or True = True
a b True and False = False
a True or False = True
a b True and True = True
a True or True = True
## Clojure
The print/println stuff in the doseq is kinda gross, but if you include them all in a single print, then the function traces are printed before the rest (since it has to evaluate them before calling print).
```Clojure
(letfn [(a [bool] (print "(a)") bool)
(b [bool] (print "(b)") bool)]
(doseq [i [true false] j [true false]]
(print i "OR" j "= ")
(println (or (a i) (b j)))
(print i "AND" j " = ")
(println (and (a i) (b j)))))
{{out}}
true OR true = (a)true
true AND true = (a)(b)true
true OR false = (a)true
true AND false = (a)(b)false
false OR true = (a)(b)true
false AND true = (a)false
false OR false = (a)(b)false
false AND false = (a)false
Common Lisp
(defun a (F)
(print 'a)
F )
(defun b (F)
(print 'b)
F )
(dolist (x '((nil nil) (nil T) (T T) (T nil)))
(format t "~%(and ~S)" x)
(and (a (car x)) (b (car(cdr x))))
(format t "~%(or ~S)" x)
(or (a (car x)) (b (car(cdr x)))))
{{out}} (and (NIL NIL)) A (or (NIL NIL)) A B (and (NIL T)) A (or (NIL T)) A B (and (T T)) A B (or (T T)) A (and (T NIL)) A B (or (T NIL)) A
D
{{trans|Python}}
import std.stdio, std.algorithm;
T a(T)(T answer) {
writefln(" # Called function a(%s) -> %s", answer, answer);
return answer;
}
T b(T)(T answer) {
writefln(" # Called function b(%s) -> %s", answer, answer);
return answer;
}
void main() {
foreach (immutable x, immutable y;
[false, true].cartesianProduct([false, true])) {
writeln("\nCalculating: r1 = a(x) && b(y)");
immutable r1 = a(x) && b(y);
writeln("Calculating: r2 = a(x) || b(y)");
immutable r2 = a(x) || b(y);
}
}
{{out}}
Calculating: r1 = a(x) && b(y)
# Called function a(false) -> false
Calculating: r2 = a(x) || b(y)
# Called function a(false) -> false
# Called function b(false) -> false
Calculating: r1 = a(x) && b(y)
# Called function a(true) -> true
# Called function b(false) -> false
Calculating: r2 = a(x) || b(y)
# Called function a(true) -> true
Calculating: r1 = a(x) && b(y)
# Called function a(false) -> false
Calculating: r2 = a(x) || b(y)
# Called function a(false) -> false
# Called function b(true) -> true
Calculating: r1 = a(x) && b(y)
# Called function a(true) -> true
# Called function b(true) -> true
Calculating: r2 = a(x) || b(y)
# Called function a(true) -> true
Delphi
Delphi supports short circuit evaluation by default. It can be turned off using the {$BOOLEVAL OFF} compiler directive.
program ShortCircuitEvaluation;
{$APPTYPE CONSOLE}
uses SysUtils;
function A(aValue: Boolean): Boolean;
begin
Writeln('a');
Result := aValue;
end;
function B(aValue: Boolean): Boolean;
begin
Writeln('b');
Result := aValue;
end;
var
i, j: Boolean;
begin
for i in [False, True] do
begin
for j in [False, True] do
begin
Writeln(Format('%s and %s = %s', [BoolToStr(i, True), BoolToStr(j, True), BoolToStr(A(i) and B(j), True)]));
Writeln;
Writeln(Format('%s or %s = %s', [BoolToStr(i, True), BoolToStr(j, True), BoolToStr(A(i) or B(j), True)]));
Writeln;
end;
end;
end.
Dyalect
{{trans|Swift}}
func a(v) {
print(nameof(a), terminator: "")
return v
}
func b(v) {
print(nameof(b), terminator: "")
return v
}
func test(i, j) {
print("Testing a(\(i)) && b(\(j))")
print("Trace: ", terminator: "")
print("\nResult: \(a(i) && b(j))")
print("Testing a(\(i)) || b(\(j))")
print("Trace: ", terminator: "")
print("\nResult: \(a(i) || b(j))")
print()
}
test(false, false)
test(false, true)
test(true, false)
test(true, true)
{{out}}
Testing a(false) && b(false)
Trace: a
Result: false
Testing a(false) || b(false)
Trace: ab
Result: false
Testing a(false) && b(true)
Trace: a
Result: false
Testing a(false) || b(true)
Trace: ab
Result: true
Testing a(true) && b(false)
Trace: ab
Result: false
Testing a(true) || b(false)
Trace: a
Result: true
Testing a(true) && b(true)
Trace: ab
Result: true
Testing a(true) || b(true)
Trace: a
Result: true
E
E defines && and || in the usual short-circuiting fashion.
def a(v) { println("a"); return v }
def b(v) { println("b"); return v }
def x := a(i) && b(j)
def y := b(i) || b(j)
Unusually, E is an expression-oriented language, and variable bindings (which are expressions) are in scope until the end of the nearest enclosing { ... } block. The combination of these features means that some semantics must be given to a binding occurring inside of a short-circuited alternative.
def x := a(i) && (def funky := b(j))
The choice we make is that funky is ordinary if the right-side expression was evaluated, and otherwise is ruined; attempts to access the variable give an error.
Elena
ELENA 4.1 :
import system'routines;
import extensions;
Func<bool, bool> a = (bool x){ console.writeLine:"a"; ^ x };
Func<bool, bool> b = (bool x){ console.writeLine:"b"; ^ x };
const bool[] boolValues = new bool[]::( false, true );
public program()
{
boolValues.forEach:(bool i)
{
boolValues.forEach:(bool j)
{
console.printLine(i," and ",j," = ",a(i) && b(j));
console.writeLine();
console.printLine(i," or ",j," = ",a(i) || b(j));
console.writeLine()
}
}
}
{{out}}
a
false and false = false
a
b
false or false = false
a
false and true = false
a
b
false or true = true
a
b
true and false = false
a
true or false = true
a
b
true and true = true
a
true or true = true
Elixir
defmodule Short_circuit do
defp a(bool) do
IO.puts "a( #{bool} ) called"
bool
end
defp b(bool) do
IO.puts "b( #{bool} ) called"
bool
end
def task do
Enum.each([true, false], fn i ->
Enum.each([true, false], fn j ->
IO.puts "a( #{i} ) and b( #{j} ) is #{a(i) and b(j)}.\n"
IO.puts "a( #{i} ) or b( #{j} ) is #{a(i) or b(j)}.\n"
end)
end)
end
end
Short_circuit.task
{{out}}
a( true ) called
b( true ) called
a( true ) and b( true ) is true.
a( true ) called
a( true ) or b( true ) is true.
a( true ) called
b( false ) called
a( true ) and b( false ) is false.
a( true ) called
a( true ) or b( false ) is true.
a( false ) called
a( false ) and b( true ) is false.
a( false ) called
b( true ) called
a( false ) or b( true ) is true.
a( false ) called
a( false ) and b( false ) is false.
a( false ) called
b( false ) called
a( false ) or b( false ) is false.
Erlang
-module( short_circuit_evaluation ).
-export( [task/0] ).
task() ->
[task_helper(X, Y) || X <- [true, false], Y <- [true, false]].
a( Boolean ) ->
io:fwrite( " a ~p~n", [Boolean] ),
Boolean.
b( Boolean ) ->
io:fwrite( " b ~p~n", [Boolean] ),
Boolean.
task_helper( Boolean1, Boolean2 ) ->
io:fwrite( "~p andalso ~p~n", [Boolean1, Boolean2] ),
io:fwrite( "=> ~p~n", [a(Boolean1) andalso b(Boolean2)] ),
io:fwrite( "~p orelse ~p~n", [Boolean1, Boolean2] ),
io:fwrite( "=> ~p~n", [a(Boolean1) orelse b(Boolean2)] ).
{{out}}
15> short_circuit_evaluation:task().
true andalso true
a true
b true
=> true
true orelse true
a true
=> true
true andalso false
a true
b false
=> false
true orelse false
a true
=> true
false andalso true
a false
=> false
false orelse true
a false
b true
=> true
false andalso false
a false
=> false
false orelse false
a false
b false
=> false
=={{header|F_Sharp|F#}}==
let a (x : bool) = printf "(a)"; x
let b (x : bool) = printf "(b)"; x
[for x in [true; false] do for y in [true; false] do yield (x, y)]
|> List.iter (fun (x, y) ->
printfn "%b AND %b = %b" x y ((a x) && (b y))
printfn "%b OR %b = %b" x y ((a x) || (b y)))
Output
(a)(b)true AND true = true
(a)true OR true = true
(a)(b)true AND false = false
(a)true OR false = true
(a)false AND true = false
(a)(b)false OR true = true
(a)false AND false = false
(a)(b)false OR false = false
Factor
&& and || perform short-circuit evaluation, while and and or do not. && and || both expect a sequence of quotations to evaluate in a short-circuit manner. They are smart combinators; that is, they infer the number of arguments taken by the quotations. If you opt not to use the smart combinators, you can also use words like 0&& and 2|| where the arity of the quotations is dictated.
USING: combinators.short-circuit.smart io prettyprint ;
IN: rosetta-code.short-circuit
: a ( ? -- ? ) "(a)" write ;
: b ( ? -- ? ) "(b)" write ;
"f && f = " write { [ f a ] [ f b ] } && .
"f || f = " write { [ f a ] [ f b ] } || .
"f && t = " write { [ f a ] [ t b ] } && .
"f || t = " write { [ f a ] [ t b ] } || .
"t && f = " write { [ t a ] [ f b ] } && .
"t || f = " write { [ t a ] [ f b ] } || .
"t && t = " write { [ t a ] [ t b ] } && .
"t || t = " write { [ t a ] [ t b ] } || .
{{out}}
f && f = (a)f
f || f = (a)(b)f
f && t = (a)f
f || t = (a)(b)t
t && f = (a)(b)f
t || f = (a)t
t && t = (a)(b)t
t || t = (a)t
Fantom
class Main
{
static Bool a (Bool value)
{
echo ("in a")
return value
}
static Bool b (Bool value)
{
echo ("in b")
return value
}
public static Void main ()
{
[false,true].each |i|
{
[false,true].each |j|
{
Bool result := a(i) && b(j)
echo ("a($i) && b($j): " + result)
result = a(i) || b(j)
echo ("a($i) || b($j): " + result)
}
}
}
}
{{out}}
in a
a(false) && b(false): false
in a
in b
a(false) || b(false): false
in a
a(false) && b(true): false
in a
in b
a(false) || b(true): true
in a
in b
a(true) && b(false): false
in a
a(true) || b(false): true
in a
in b
a(true) && b(true): true
in a
a(true) || b(true): true
=={{header|Fōrmulæ}}==
In [https://wiki.formulae.org/Short-circuit_evaluation this] page you can see the solution of this task.
Fōrmulæ programs are not textual, visualization/edition of programs is done showing/manipulating structures but not text ([http://wiki.formulae.org/Editing_F%C5%8Drmul%C3%A6_expressions more info]). Moreover, there can be multiple visual representations of the same program. Even though it is possible to have textual representation —i.e. XML, JSON— they are intended for transportation effects more than visualization and edition.
The option to show Fōrmulæ programs and their results is showing images. Unfortunately images cannot be uploaded in Rosetta Code.
Forth
\ Short-circuit evaluation definitions from Wil Baden, with minor name changes
: ENDIF postpone THEN ; immediate
: COND 0 ; immediate
: ENDIFS BEGIN DUP WHILE postpone ENDIF REPEAT DROP ; immediate
: ORELSE s" ?DUP 0= IF" evaluate ; immediate
: ANDIF s" DUP IF DROP" evaluate ; immediate
: .bool IF ." true " ELSE ." false " THEN ;
: A ." A=" DUP .bool ;
: B ." B=" DUP .bool ;
: test
CR
1 -1 DO 1 -1 DO
COND I A ANDIF J B ENDIFS ." ANDIF=" .bool CR
COND I A ORELSE J B ENDIFS ." ORELSE=" .bool CR
LOOP LOOP ;
\ An alternative based on explicitly short-circuiting conditionals, Dave Keenan
: END-PRIOR-IF 1 CS-ROLL postpone ENDIF ; immediate
: test
CR
1 -1 DO 1 -1 DO
I A IF J B IF 1 ELSE END-PRIOR-IF 0 ENDIF ." ANDIF=" .bool CR
I A 0= IF J B IF END-PRIOR-IF 1 ELSE 0 ENDIF ." ORELSE=" .bool CR
LOOP LOOP ;
{{out}}
A=true B=true ANDIF=true
A=true ORELSE=true
A=false ANDIF=false
A=false B=true ORELSE=true
A=true B=false ANDIF=false
A=true ORELSE=true
A=false ANDIF=false
A=false B=false ORELSE=false
Fortran
{{works with|Fortran|90 and later}}
Using an IF .. THEN .. ELSE construct
program Short_Circuit_Eval
implicit none
logical :: x, y
logical, dimension(2) :: l = (/ .false., .true. /)
integer :: i, j
do i = 1, 2
do j = 1, 2
write(*, "(a,l1,a,l1,a)") "Calculating x = a(", l(i), ") and b(", l(j), ")"
! a AND b
x = a(l(i))
if(x) then
x = b(l(j))
write(*, "(a,l1)") "x = ", x
else
write(*, "(a,l1)") "x = ", x
end if
write(*,*)
write(*, "(a,l1,a,l1,a)") "Calculating y = a(", l(i), ") or b(", l(j), ")"
! a OR b
y = a(l(i))
if(y) then
write(*, "(a,l1)") "y = ", y
else
y = b(l(j))
write(*, "(a,l1)") "y = ", y
end if
write(*,*)
end do
end do
contains
function a(value)
logical :: a
logical, intent(in) :: value
a = value
write(*, "(a,l1,a)") "Called function a(", value, ")"
end function
function b(value)
logical :: b
logical, intent(in) :: value
b = value
write(*, "(a,l1,a)") "Called function b(", value, ")"
end function
end program
{{out}}
Calculating x = a(F) and b(F)
Called function a(F)
x = F
Calculating y = a(F) or b(F)
Called function a(F)
Called function b(F)
y = F
Calculating x = a(F) and b(T)
Called function a(F)
x = F
Calculating y = a(F) or b(T)
Called function a(F)
Called function b(T)
y = T
Calculating x = a(T) and b(F)
Called function a(T)
Called function b(F)
x = F
Calculating y = a(T) or b(F)
Called function a(T)
y = T
Calculating x = a(T) and b(T)
Called function a(T)
Called function b(T)
x = T
Calculating y = a(T) or b(T)
Called function a(T)
y = T
FreeBASIC
' FB 1.05.0 Win64
Function a(p As Boolean) As Boolean
Print "a() called"
Return p
End Function
Function b(p As Boolean) As Boolean
Print "b() called"
Return p
End Function
Dim As Boolean i, j, x, y
i = False
j = True
Print "Without short-circuit evaluation :"
Print
x = a(i) And b(j)
y = a(i) Or b(j)
Print "x = "; x; " y = "; y
Print
Print "With short-circuit evaluation :"
Print
x = a(i) AndAlso b(j) '' b(j) not called as a(i) = false and so x must be false
y = a(i) OrElse b(j) '' b(j) still called as can't determine y unless it is
Print "x = "; x; " y = "; y
Print
Print "Press any key to quit"
Sleep
{{out}}
Without short-circuit evaluation :
a() called
b() called
a() called
b() called
x = false y = true
With short-circuit evaluation :
a() called
a() called
b() called
x = false y = true
Go
Short circuit operators are
package main
import "fmt"
func a(v bool) bool {
fmt.Print("a")
return v
}
func b(v bool) bool {
fmt.Print("b")
return v
}
func test(i, j bool) {
fmt.Printf("Testing a(%t) && b(%t)\n", i, j)
fmt.Print("Trace: ")
fmt.Println("\nResult:", a(i) && b(j))
fmt.Printf("Testing a(%t) || b(%t)\n", i, j)
fmt.Print("Trace: ")
fmt.Println("\nResult:", a(i) || b(j))
fmt.Println("")
}
func main() {
test(false, false)
test(false, true)
test(true, false)
test(true, true)
}
{{out}}
Testing a(false) && b(false)
Trace: a
Result: false
Testing a(false) || b(false)
Trace: ab
Result: false
Testing a(false) && b(true)
Trace: a
Result: false
Testing a(false) || b(true)
Trace: ab
Result: true
Testing a(true) && b(false)
Trace: ab
Result: false
Testing a(true) || b(false)
Trace: a
Result: true
Testing a(true) && b(true)
Trace: ab
Result: true
Testing a(true) || b(true)
Trace: a
Result: true
Groovy
Like all C-based languages (of which I am aware), Groovy short-circuits the logical and (
def f = { println ' AHA!'; it instanceof String }
def g = { printf ('%5d ', it); it > 50 }
println 'bitwise'
assert g(100) & f('sss')
assert g(2) | f('sss')
assert ! (g(1) & f('sss'))
assert g(200) | f('sss')
println '''
logical'''
assert g(100) && f('sss')
assert g(2) || f('sss')
assert ! (g(1) && f('sss'))
assert g(200) || f('sss')
{{out}}
bitwise
100 AHA!
2 AHA!
1 AHA!
200 AHA!
logical
100 AHA!
2 AHA!
1 200
Haskell
[[Lazy evaluation]] makes it possible for user-defined functions to be short-circuited. An expression will not be evaluated as long as it is not [[pattern matching|pattern matched]]:
module ShortCircuit where
import Prelude hiding ((&&), (||))
import Debug.Trace
False && _ = False
True && False = False
_ && _ = True
True || _ = True
False || True = True
_ || _ = False
a p = trace ("<a " ++ show p ++ ">") p
b p = trace ("<b " ++ show p ++ ">") p
main = mapM_ print ( [ a p || b q | p <- [False, True], q <- [False, True] ]
++ [ a p && b q | p <- [False, True], q <- [False, True] ])
{{out}}
<a False>
<b False>
False
<a False>
<b True>
True
<a True>
True
<a True>
True
<a False>
False
<a False>
False
<a True>
<b False>
False
<a True>
<b True>
True
One can force the right-hand arguemnt to be evaluated first be using the alternate definitions:
_ && False = False
False && True = False
_ && _ = True
_ || True = True
True || False = True
_ || _ = False
{{out}}
<b False>
<a False>
False
<b True>
True
<b False>
<a True>
True
<b True>
True
<b False>
False
<b True>
<a False>
False
<b False>
False
<b True>
<a True>
True
The order of evaluation (in this case the original order again) can be seen in a more explicit form by [[syntactic sugar|desugaring]] the pattern matching:
p && q = case p of
False -> False
_ -> case q of
False -> False
_ -> True
p || q = case p of
True -> True
_ -> case q of
True -> True
_ -> False
=={{header|Icon}} and {{header|Unicon}}== The entire concept of using 'boolean' values for logic control runs counter to the philosophy of Icon. Instead Icon has success (something that returns a result) and failure which is really a signal. The concept is similar to that used in [[:Category:SNOBOL4|SNOBOL4]] and [[:Category:Lisp|Lisp]] and far more potent than passing around and testing booleans. There is no way to pass around a 'false' value in that sense. Icon does have facilities for dealing with bits inside integers but these would not normally be used for control purposes. Because failure is a signal control is always evaluated in a short-circuit manner. One consequence of this is that an expression "i < j" doesn't return a boolean value, instead it returns the value of j. While this may seem odd at first it allows for elegant expressions like "i < j < k". Another benefit is that there is no need for programmers to devote effort to staying inside the bounds of any data type. For instance, if you loop and iterate beyond bounds the expression simply fails and the loop ends.
While this task could be written literally, it would be more beneficial to show how an Icon programmer would approach the same problem. Icon extends the idea short circuit evaluation with the ability for expressions to generate alternate results only if needed. For more information see [[Icon%2BUnicon/Intro#Program_Flow_and_Control|Failure is an option, Everything Returns a Value Except when it Doesn't, and Goal-Directed Evaluation and Generators]]. Consequently some small liberties will be taken with this task:
- Since any result means an expression succeeded and is hence true, we can use any value. In this example our choice will be determined by how we deal with 'false'.
- The inability to pass a 'false' value is a challenge. At first glance we might try &null, similar to Lisp, but there is no canonical true. Also &null produces a result, so strictly speaking it could be 'true' as well. A good example of this is that an expression like " not expr " returns null if 'expr' fails.
- For this example we will define two procedures 'true' and 'false'. Because Icon treats procedures as a data type we can assign them and invoke them indirectly via the variable name they are assigned to. We can write " i := true " and later invoke 'true' via " i() ".
- Rather than have the tasks print their own name, we will just utilize built-in tracing which will be more informative. This use of procedures as values is somewhat contrived but serves us well for demonstration purposes. In practice this approach would be strained since failure results aren't re-captured as values (and can't easily be).
procedure main()
&trace := -1 # ensures functions print their names
every (i := false | true ) & ( j := false | true) do {
write("i,j := ",image(i),", ",image(j))
write("i & j:")
x := i() & j() # invoke true/false
write("i | j:")
y := i() | j() # invoke true/false
}
end
procedure true() #: succeeds always (returning null)
return
end
procedure false() #: fails always
fail # for clarity but not needed as running into end has the same effect
end
Sample output for a single case:
i,j := procedure true, procedure false
i & j:
Shortcircuit.icn: 8 | true()
Shortcircuit.icn: 16 | true returned &null
Shortcircuit.icn: 8 | false()
Shortcircuit.icn: 20 | false failed
i | j:
Shortcircuit.icn: 10 | true()
Shortcircuit.icn: 16 | true returned &null
i,j := procedure true, procedure true
Io
{{trans|Ruby}}
a := method(bool,
writeln("a(#{bool}) called." interpolate)
bool
)
b := method(bool,
writeln("b(#{bool}) called." interpolate)
bool
)
list(true,false) foreach(avalue,
list(true,false) foreach(bvalue,
x := a(avalue) and b(bvalue)
writeln("x = a(#{avalue}) and b(#{bvalue}) is #{x}" interpolate)
writeln
y := a(avalue) or b(bvalue)
writeln("y = a(#{avalue}) or b(#{bvalue}) is #{y}" interpolate)
writeln
)
)
{{output}}
a(true) called.
b(true) called.
x = a(true) and b(true) is true
a(true) called.
y = a(true) or b(true) is true
a(true) called.
b(false) called.
x = a(true) and b(false) is false
a(true) called.
y = a(true) or b(false) is true
a(false) called.
x = a(false) and b(true) is false
a(false) called.
b(true) called.
y = a(false) or b(true) is true
a(false) called.
x = a(false) and b(false) is false
a(false) called.
b(false) called.
y = a(false) or b(false) is false
J
See the J wiki entry on [[j:Essays/Short Circuit Boolean|short circuit booleans]].
labeled=:1 :'[ smoutput@,&":~&m'
A=: 'A ' labeled
B=: 'B ' labeled
and=: ^:
or=: 2 :'u^:(-.@v)'
{{out|Example}}
(A and B) 1
B 1
A 1
1
(A and B) 0
B 0
0
(A or B) 1
B 1
1
(A or B) 0
B 0
A 0
0
Note that J evaluates right-to-left.
Note also that both functions take the same argument (which might make this less than ideal for some purposes, but trying micromanage flow of control is usually counter-productive in J in much the way that global values can be counter-productive in an object oriented environment. When you are processing a large set of array data, flow of control can only make sense when it is relevant to all of the data being processed -- if you want to manage flow of control which is not relevant to the entire set of data being processed you might artificially reduce the amount of data being processed, along the lines of an SQL cursor).
Java
In Java the boolean operators && and || are short circuit operators. The eager operator counterparts are & and |.
public class ShortCirc {
public static void main(String[] args){
System.out.println("F and F = " + (a(false) && b(false)) + "\n");
System.out.println("F or F = " + (a(false) || b(false)) + "\n");
System.out.println("F and T = " + (a(false) && b(true)) + "\n");
System.out.println("F or T = " + (a(false) || b(true)) + "\n");
System.out.println("T and F = " + (a(true) && b(false)) + "\n");
System.out.println("T or F = " + (a(true) || b(false)) + "\n");
System.out.println("T and T = " + (a(true) && b(true)) + "\n");
System.out.println("T or T = " + (a(true) || b(true)) + "\n");
}
public static boolean a(boolean a){
System.out.println("a");
return a;
}
public static boolean b(boolean b){
System.out.println("b");
return b;
}
}
{{out}}
a
F and F = false
a
b
F or F = false
a
F and T = false
a
b
F or T = true
a
b
T and F = false
a
T or F = true
a
b
T and T = true
a
T or T = true
JavaScript
Short-circuiting evaluation of boolean expressions has been the default since the first versions of JavaScript.
(function () {
'use strict';
function a(bool) {
console.log('a -->', bool);
return bool;
}
function b(bool) {
console.log('b -->', bool);
return bool;
}
var x = a(false) && b(true),
y = a(true) || b(false),
z = true ? a(true) : b(false);
return [x, y, z];
})();
The console log shows that in each case (the binding of all three values), only the left-hand part of the expression (the application of ''a(expr)'') was evaluated – ''b(expr)'' was skipped by logical short-circuiting.
{{Out}}
Console:
/* a --> false */
/* a --> true */
/* a --> true */
Return value:
[false, true, true]
jq
jq's 'and' and 'or' are short-circuit operators. The following demonstration, which follows the "awk" example above, requires a version of jq with the built-in filter 'stderr'.
def a(x): " a(\(x))" | stderr | x;
def b(y): " b(\(y))" | stderr | y;
"and:", (a(true) and b(true)),
"or:", (a(true) or b(true)),
"and:", (a(false) and b(true)),
"or:", (a(false) or b(true))
{{out}}
$ jq -r -n -f Short-circuit-evaluation.jq
and:
" a(true)"
" b(true)"
true
or:
" a(true)"
true
and:
" a(false)"
false
or:
" a(false)"
" b(true)"
true
Julia
Julia does have short-circuit evaluation, which works just as you expect it to:
a(x) = (println("\t# Called a($x)"); return x)
b(x) = (println("\t# Called b($x)"); return x)
for i in [true,false], j in [true, false]
println("\nCalculating: x = a($i) && b($j)"); x = a(i) && b(j)
println("\tResult: x = $x")
println("\nCalculating: y = a($i) || b($j)"); y = a(i) || b(j)
println("\tResult: y = $y")
end
{{out}}
Calculating: x = a(true) && b(true)
# Called a(true)
# Called b(true)
Result: x = true
Calculating: y = a(true) || b(true)
# Called a(true)
Result: y = true
Calculating: x = a(true) && b(false)
# Called a(true)
# Called b(false)
Result: x = false
Calculating: y = a(true) || b(false)
# Called a(true)
Result: y = true
Calculating: x = a(false) && b(true)
# Called a(false)
Result: x = false
Calculating: y = a(false) || b(true)
# Called a(false)
# Called b(true)
Result: y = true
Calculating: x = a(false) && b(false)
# Called a(false)
Result: x = false
Calculating: y = a(false) || b(false)
# Called a(false)
# Called b(false)
Result: y = false
Kotlin
// version 1.1.2
fun a(v: Boolean): Boolean {
println("'a' called")
return v
}
fun b(v: Boolean): Boolean {
println("'b' called")
return v
}
fun main(args: Array<String>){
val pairs = arrayOf(Pair(true, true), Pair(true, false), Pair(false, true), Pair(false, false))
for (pair in pairs) {
val x = a(pair.first) && b(pair.second)
println("${pair.first} && ${pair.second} = $x")
val y = a(pair.first) || b(pair.second)
println("${pair.first} || ${pair.second} = $y")
println()
}
}
{{out}}
'a' called
'b' called
true && true = true
'a' called
true || true = true
'a' called
'b' called
true && false = false
'a' called
true || false = true
'a' called
false && true = false
'a' called
'b' called
false || true = true
'a' called
false && false = false
'a' called
'b' called
false || false = false
Liberty BASIC
LB does not have short-circuit evaluation. Implemented with IFs.
print "AND"
for i = 0 to 1
for j = 0 to 1
print "a("; i; ") AND b( "; j; ")"
res =a( i) 'call always
if res <>0 then 'short circuit if 0
res = b( j)
end if
print "=>",res
next
next
print "---------------------------------"
print "OR"
for i = 0 to 1
for j = 0 to 1
print "a("; i; ") OR b("; j; ")"
res =a( i) 'call always
if res = 0 then 'short circuit if <>0
res = b( j)
end if
print "=>", res
next
next
'----------------------------------------
function a( t)
print ,"calls func a"
a = t
end function
function b( t)
print ,"calls func b"
b = t
end function
{{out}}
AND
a(0) AND b( 0)
calls func a
=> 0
a(0) AND b( 1)
calls func a
=> 0
a(1) AND b( 0)
calls func a
calls func b
=> 0
a(1) AND b( 1)
calls func a
calls func b
=> 1
---------------------------------
OR
a(0) OR b(0)
calls func a
calls func b
=> 0
a(0) OR b(1)
calls func a
calls func b
=> 1
a(1) OR b(0)
calls func a
=> 1
a(1) OR b(1)
calls func a
=> 1
LiveCode
Livecode uses short-circuit evaluation.
global outcome
function a bool
put "a called with" && bool & cr after outcome
return bool
end a
function b bool
put "b called with" && bool & cr after outcome
return bool
end b
on mouseUp
local tExp
put empty into outcome
repeat for each item op in "and,or"
repeat for each item x in "true,false"
put merge("a([[x]]) [[op]] b([[x]])") into tExp
put merge(tExp && "is [[" & tExp & "]]") & cr after outcome
put merge("a([[x]]) [[op]] b([[not x]])") into tExp
put merge(tExp && "is [[" & tExp & "]]") & cr after outcome
end repeat
put cr after outcome
end repeat
put outcome
end mouseUp
Logo
The AND and OR predicates may take either expressions which are all evaluated beforehand, or lists which are short-circuit evaluated from left to right only until the overall value of the expression can be determined.
and [notequal? :x 0] [1/:x > 3]
(or [:x < 0] [:y < 0] [sqrt :x + sqrt :y < 3])
Lua
function a(i)
print "Function a(i) called."
return i
end
function b(i)
print "Function b(i) called."
return i
end
i = true
x = a(i) and b(i); print ""
y = a(i) or b(i); print ""
i = false
x = a(i) and b(i); print ""
y = a(i) or b(i)
Maple
Built-in short circuit evaluation
a := proc(bool)
printf("a is called->%s\n", bool):
return bool:
end proc:
b := proc(bool)
printf("b is called->%s\n", bool):
return bool:
end proc:
for i in [true, false] do
for j in [true, false] do
printf("calculating x := a(i) and b(j)\n"):
x := a(i) and b(j):
printf("calculating x := a(i) or b(j)\n"):
y := a(i) or b(j):
od:
od:
{{Out|Output}}
calculating x := a(i) and b(j)
a is called->true
b is called->true
calculating x := a(i) or b(j)
a is called->true
calculating x := a(i) and b(j)
a is called->true
b is called->false
calculating x := a(i) or b(j)
a is called->true
calculating x := a(i) and b(j)
a is called->false
calculating x := a(i) or b(j)
a is called->false
b is called->true
calculating x := a(i) and b(j)
a is called->false
calculating x := a(i) or b(j)
a is called->false
b is called->false
Mathematica
Mathematica has built-in short-circuit evaluation of logical expressions.
a[in_] := (Print["a"]; in)
b[in_] := (Print["b"]; in)
a[False] && b[True]
a[True] || b[False]
Evaluation of the preceding code gives:
a
False
a
True
Whereas evaluating this:
a[True] && b[False]
Gives:
a
b
False
=={{header|MATLAB}} / {{header|Octave}}== Short-circuit evalation is done in logical AND (&&) and logical OR (||) operators:
function x=a(x)
printf('a: %i\n',x);
end;
function x=b(x)
printf('b: %i\n',x);
end;
a(1) && b(1)
a(0) && b(1)
a(1) || b(1)
a(0) || b(1)
{{out}}
a(1) && b(1);
a: 1
b: 1
> a(0) && b(1);
a: 0
> a(1) || b(1);
a: 1
> a(0) || b(1);
a: 0
b: 1
=={{header|Modula-2}}==
MODULE ShortCircuit;
FROM FormatString IMPORT FormatString;
FROM Terminal IMPORT WriteString,WriteLn,ReadChar;
PROCEDURE a(v : BOOLEAN) : BOOLEAN;
VAR buf : ARRAY[0..63] OF CHAR;
BEGIN
FormatString(" # Called function a(%b)\n", buf, v);
WriteString(buf);
RETURN v
END a;
PROCEDURE b(v : BOOLEAN) : BOOLEAN;
VAR buf : ARRAY[0..63] OF CHAR;
BEGIN
FormatString(" # Called function b(%b)\n", buf, v);
WriteString(buf);
RETURN v
END b;
PROCEDURE Print(x,y : BOOLEAN);
VAR buf : ARRAY[0..63] OF CHAR;
VAR temp : BOOLEAN;
BEGIN
FormatString("a(%b) AND b(%b)\n", buf, x, y);
WriteString(buf);
temp := a(x) AND b(y);
FormatString("a(%b) OR b(%b)\n", buf, x, y);
WriteString(buf);
temp := a(x) OR b(y);
WriteLn;
END Print;
BEGIN
Print(FALSE,FALSE);
Print(FALSE,TRUE);
Print(TRUE,TRUE);
Print(TRUE,FALSE);
ReadChar
END ShortCircuit.
MUMPS
MUMPS evaluates every expression it encounters, so we have to use conditional statements to do a short circuiting of the expensive second task.
SSEVAL1(IN)
WRITE !,?10,$STACK($STACK,"PLACE")
QUIT IN
SSEVAL2(IN)
WRITE !,?10,$STACK($STACK,"PLACE")
QUIT IN
SSEVAL3
NEW Z
WRITE "1 AND 1"
SET Z=$$SSEVAL1(1) SET:Z Z=Z&$$SSEVAL2(1)
WRITE !,$SELECT(Z:"TRUE",1:"FALSE")
WRITE !!,"0 AND 1"
SET Z=$$SSEVAL1(0) SET:Z Z=Z&$$SSEVAL2(1)
WRITE !,$SELECT(Z:"TRUE",1:"FALSE")
WRITE !!,"1 OR 1"
SET Z=$$SSEVAL1(1) SET:'Z Z=Z!$$SSEVAL2(1)
WRITE !,$SELECT(Z:"TRUE",1:"FALSE")
WRITE !!,"0 OR 1"
SET Z=$$SSEVAL1(0) SET:'Z Z=Z!$$SSEVAL2(1)
WRITE !,$SELECT(Z:"TRUE",1:"FALSE")
KILL Z
QUIT
{{out}}
USER>D SSEVAL3^ROSETTA
1 AND 1
SSEVAL1+1^ROSETTA +3
SSEVAL2+1^ROSETTA +3
TRUE
0 AND 1
SSEVAL1+1^ROSETTA +3
FALSE
1 OR 1
SSEVAL1+1^ROSETTA +3
TRUE
0 OR 1
SSEVAL1+1^ROSETTA +3
SSEVAL2+1^ROSETTA +3
TRUE
Nemerle
using System.Console;
class ShortCircuit
{
public static a(x : bool) : bool
{
WriteLine("a");
x
}
public static b(x : bool) : bool
{
WriteLine("b");
x
}
public static Main() : void
{
def t = true;
def f = false;
WriteLine("True && True : {0}", a(t) && b(t));
WriteLine("True && False: {0}", a(t) && b(f));
WriteLine("False && True : {0}", a(f) && b(t));
WriteLine("False && False: {0}", a(f) && b(f));
WriteLine("True || True : {0}", a(t) || b(t));
WriteLine("True || False: {0}", a(t) || b(f));
WriteLine("False || True : {0}", a(f) || b(t));
WriteLine("False || False: {0}", a(f) || b(f));
}
}
{{out}}
## NetRexx
{{trans|ooRexx}}
Like [[OoRexx]], [[NetRexx]] allows a list of expressions in the condition part of <tt>If</tt> and <tt>When</tt>. Evaluation ends with the first of these expressions resulting in <tt>boolean true</tt>.
```NetRexx
/* NetRexx */
options replace format comments java crossref symbols nobinary
Parse Version v
Say 'Version='v
If a() | b() Then Say 'a and b are true'
If \a() | b() Then Say 'Surprise'
Else Say 'ok'
If a(), b() Then Say 'a is true'
If \a(), b() Then Say 'Surprise'
Else Say 'ok: \\a() is false'
Select
When \a(), b() Then Say 'Surprise'
Otherwise Say 'ok: \\a() is false (Select)'
End
Return
method a private static binary returns boolean
state = Boolean.TRUE.booleanValue()
Say '--a returns' state
Return state
method b private static binary returns boolean
state = Boolean.TRUE.booleanValue()
Say '--b returns' state
Return state
{{out}}
Version=NetRexx 3.03 11 Jun 2014
--a returns 1
--b returns 1
a and b are true
--a returns 1
--b returns 1
Surprise
--a returns 1
a is true
--a returns 1
--b returns 1
Surprise
--a returns 1
--b returns 1
Surprise
Nim
proc a(x): bool =
echo "a called"
result = x
proc b(x): bool =
echo "b called"
result = x
let x = a(false) and b(true) # echoes "a called"
let y = a(true) or b(true) # echoes "a called"
Objeck
In Objeck the Boolean operators & and | short circuit.
class ShortCircuit {
function : a(a : Bool) ~ Bool {
"a"->PrintLine();
return a;
}
function : b(b : Bool) ~ Bool {
"b"->PrintLine();
return b;
}
function : Main(args : String[]) ~ Nil {
result := a(false) & b(false);
"F and F = {$result}"->PrintLine();
result := a(false) | b(false);
"F or F = {$result}"->PrintLine();
result := a(false) & b(true);
"F and T = {$result}"->PrintLine();
result := a(false) | b(true);
"F or T = {$result}"->PrintLine();
result := a(true) & b(false);
"T and F = {$result}"->PrintLine();
result := a(true) | b(false);
"T or F = {$result}"->PrintLine();
result := a(true) & b(true);
"T and T = {$result}"->PrintLine();
result := a(true) | b(true);
"T or T = {$result}"->PrintLine();
}
}
OCaml
let a r = print_endline " > function a called"; r
let b r = print_endline " > function b called"; r
let test_and b1 b2 =
Printf.printf "# testing (%b && %b)\n" b1 b2;
ignore (a b1 && b b2)
let test_or b1 b2 =
Printf.printf "# testing (%b || %b)\n" b1 b2;
ignore (a b1 || b b2)
let test_this test =
test true true;
test true false;
test false true;
test false false;
;;
let () =
print_endline "
### = Testing and =
";
test_this test_and;
print_endline "
### = Testing or =
";
test_this test_or;
;;
{{out}}
= Testing and =
testing (true && true)
function a called function b called
testing (true && false)
function a called function b called
testing (false && true)
function a called
testing (false && false)
function a called
= Testing or =
testing (true || true)
function a called
testing (true || false)
function a called
testing (false || true)
function a called function b called
testing (false || false)
function a called function b called
ooRexx
ooRexx allows a list of expressions in the condition part of If and When. Evaluation ends with the first of these expressions resulting in .false (or 0).
Parse Version v
Say 'Version='v
If a() | b() Then Say 'a and b are true'
If \a() | b() Then Say 'Surprise'
Else Say 'ok'
If a(), b() Then Say 'a is true'
If \a(), b() Then Say 'Surprise'
Else Say 'ok: \a() is false'
Select
When \a(), b() Then Say 'Surprise'
Otherwise Say 'ok: \a() is false (Select)'
End
Exit
a: Say 'a returns .true'; Return .true
b: Say 'b returns 1'; Return 1
{{out}}
Version=REXX-ooRexx_4.2.0(MT)_32-bit 6.04 22 Feb 2014
a returns .true
b returns 1
a and b are true
a returns .true
b returns 1
Surprise
a returns .true
b returns 1
a is true
a returns .true
ok: \a() is false
a returns .true
ok: \a() is false (Select)
Oz
Oz' andthen and orelse operators are short-circuiting, as indicated by their name. The library functions Bool.and and Bool.or are not short-circuiting, on the other hand.
declare
fun {A Answer}
AnswerS = {Value.toVirtualString Answer 1 1}
in
{System.showInfo " % Called function {A "#AnswerS#"} -> "#AnswerS}
Answer
end
fun {B Answer}
AnswerS = {Value.toVirtualString Answer 1 1}
in
{System.showInfo " % Called function {B "#AnswerS#"} -> "#AnswerS}
Answer
end
in
for I in [false true] do
for J in [false true] do
X Y
in
{System.showInfo "\nCalculating: X = {A I} andthen {B J}"}
X = {A I} andthen {B J}
{System.showInfo "Calculating: Y = {A I} orelse {B J}"}
Y = {A I} orelse {B J}
end
end
{{out}}
Calculating: X = {A I} andthen {B J}
% Called function {A false} -> false
Calculating: Y = {A I} orelse {B J}
% Called function {A false} -> false
% Called function {B false} -> false
Calculating: X = {A I} andthen {B J}
% Called function {A false} -> false
Calculating: Y = {A I} orelse {B J}
% Called function {A false} -> false
% Called function {B true} -> true
Calculating: X = {A I} andthen {B J}
% Called function {A true} -> true
% Called function {B false} -> false
Calculating: Y = {A I} orelse {B J}
% Called function {A true} -> true
Calculating: X = {A I} andthen {B J}
% Called function {A true} -> true
% Called function {B true} -> true
Calculating: Y = {A I} orelse {B J}
% Called function {A true} -> true
PARI/GP
Note that | and & are deprecated versions of the GP short-circuit operators.
a(n)={
print(a"("n")");
a
};
b(n)={
print("b("n")");
n
};
or(A,B)={
a(A) || b(B)
};
and(A,B)={
a(A) && b(B)
};
Pascal
Standard Pascal
Standard Pascal doesn't have native short-circuit evaluation.
program shortcircuit(output);
function a(value: boolean): boolean;
begin
writeln('a(', value, ')');
a := value
end;
function b(value:boolean): boolean;
begin
writeln('b(', value, ')');
b := value
end;
procedure scandor(value1, value2: boolean);
var
result: boolean;
begin
{and}
if a(value1)
then
result := b(value2)
else
result := false;
writeln(value1, ' and ', value2, ' = ', result);
{or}
if a(value1)
then
result := true
else
result := b(value2)
writeln(value1, ' or ', value2, ' = ', result);
end;
begin
scandor(false, false);
scandor(false, true);
scandor(true, false);
scandor(true, true);
end.
Turbo Pascal
Turbo Pascal allows short circuit evaluation with a compiler switch:
program shortcircuit;
function a(value: boolean): boolean;
begin
writeln('a(', value, ')');
a := value;
end;
function b(value:boolean): boolean;
begin
writeln('b(', value, ')');
b := value;
end;
{$B-} {enable short circuit evaluation}
procedure scandor(value1, value2: boolean);
var
result: boolean;
begin
result := a(value1) and b(value);
writeln(value1, ' and ', value2, ' = ', result);
result := a(value1) or b(value2);
writeln(value1, ' or ', value2, ' = ', result);
end;
begin
scandor(false, false);
scandor(false, true);
scandor(true, false);
scandor(true, true);
end.
Extended Pascal
The extended Pascal standard introduces the operators and_then and or_else for short-circuit evaluation.
program shortcircuit(output);
function a(value: boolean): boolean;
begin
writeln('a(', value, ')');
a := value
end;
function b(value:boolean): boolean;
begin
writeln('b(', value, ')');
b := value
end;
procedure scandor(value1, value2: boolean);
var
result: integer;
begin
result := a(value1) and_then b(value)
writeln(value1, ' and ', value2, ' = ', result);
result := a(value1) or_else b(value2);
writeln(value1, ' or ', value2, ' = ', result)
end;
begin
scandor(false, false);
scandor(false, true);
scandor(true, false);
scandor(true, true);
end.
Note: GNU Pascal allows and then and or else as alternatives to and_then and or_else.
Perl
Perl uses short-circuit boolean evaluation.
sub a { print 'A'; return $_[0] }
sub b { print 'B'; return $_[0] }
# Test-driver
sub test {
for my $op ('&&','||') {
for (qw(1,1 1,0 0,1 0,0)) {
my ($x,$y) = /(.),(.)/;
print my $str = "a($x) $op b($y)", ': ';
eval $str; print "\n"; } }
}
# Test and display
test();
{{out}}
a(1) && b(1): AB
a(1) && b(0): AB
a(0) && b(1): A
a(0) && b(0): A
a(1) || b(1): A
a(1) || b(0): A
a(0) || b(1): AB
a(0) || b(0): AB
Perl 6
{{Works with|rakudo|2018.03}}
use MONKEY-SEE-NO-EVAL;
sub a ($p) { print 'a'; $p }
sub b ($p) { print 'b'; $p }
for 1, 0 X 1, 0 -> ($p, $q) {
for '&&', '||' -> $op {
my $s = "a($p) $op b($q)";
print "$s: ";
EVAL $s;
print "\n";
}
}
{{out}}
a(1) && b(1): ab
a(1) || b(1): a
a(1) && b(0): ab
a(1) || b(0): a
a(0) && b(1): a
a(0) || b(1): ab
a(0) && b(0): a
a(0) || b(0): ab
Phix
In Phix all expressions are short circuited
function a(integer i)
printf(1,"a ")
return i
end function
function b(integer i)
printf(1,"b ")
return i
end function
for z=0 to 1 do
for i=0 to 1 do
for j=0 to 1 do
if z then
printf(1,"a(%d) and b(%d) ",{i,j})
printf(1," => %d\n",a(i) and b(j))
else
printf(1,"a(%d) or b(%d) ",{i,j})
printf(1," => %d\n",a(i) or b(j))
end if
end for
end for
end for
{{Out}}
a(0) or b(0) a b => 0
a(0) or b(1) a b => 1
a(1) or b(0) a => 1
a(1) or b(1) a => 1
a(0) and b(0) a => 0
a(0) and b(1) a => 0
a(1) and b(0) a b => 0
a(1) and b(1) a b => 1
PicoLisp
(de a (F)
(msg 'a)
F )
(de b (F)
(msg 'b)
F )
(mapc
'((I J)
(for Op '(and or)
(println I Op J '-> (Op (a I) (b J))) ) )
'(NIL NIL T T)
'(NIL T NIL T) )
{{out}}
a
NIL and NIL -> NIL
a
b
NIL or NIL -> NIL
a
NIL and T -> NIL
a
b
NIL or T -> T
a
b
T and NIL -> NIL
a
T or NIL -> T
a
b
T and T -> T
a
T or T -> T
Pike
int(0..1) a(int(0..1) i)
{
write(" a\n");
return i;
}
int(0..1) b(int(0..1) i)
{
write(" b\n");
return i;
}
foreach(({ ({ false, false }), ({ false, true }), ({ true, true }), ({ true, false }) });; array(int) args)
{
write(" %d && %d\n", @args);
a(args[0]) && b(args[1]);
write(" %d || %d\n", @args);
a(args[0]) || b(args[1]);
}
{{out}}
0 && 0
a
0 || 0
a
b
0 && 1
a
0 || 1
a
b
1 && 1
a
b
1 || 1
a
1 && 0
a
b
1 || 0
a
PL/I
short_circuit_evaluation:
procedure options (main);
declare (true initial ('1'b), false initial ('0'b) ) bit (1);
declare (i, j, x, y) bit (1);
a: procedure (bv) returns (bit(1));
declare bv bit(1);
put ('Procedure ' || procedurename() || ' called.');
return (bv);
end a;
b: procedure (bv) returns (bit(1));
declare bv bit(1);
put ('Procedure ' || procedurename() || ' called.');
return (bv);
end b;
do i = true, false;
do j = true, false;
put skip(2) list ('Evaluating x with <a> with ' || i || ' and <b> with ' || j);
put skip;
if a(i) then
x = b(j);
else
x = false;
put skip data (x);
put skip(2) list ('Evaluating y with <a> with ' || i || ' and <b> with ' || j);
put skip;
if a(i) then
y = true;
else
y = b(j);
put skip data (y);
end;
end;
end short_circuit_evaluation;
{{out|Results}}
Evaluating x with <a> with 1 and <b> with 1
Procedure A called. Procedure B called.
X='1'B;
Evaluating y with <a> with 1 and <b> with 1
Procedure A called.
Y='1'B;
Evaluating x with <a> with 1 and <b> with 0
Procedure A called. Procedure B called.
X='0'B;
Evaluating y with <a> with 1 and <b> with 0
Procedure A called.
Y='1'B;
Evaluating x with <a> with 0 and <b> with 1
Procedure A called.
X='0'B;
Evaluating y with <a> with 0 and <b> with 1
Procedure A called. Procedure B called.
Y='1'B;
Evaluating x with <a> with 0 and <b> with 0
Procedure A called.
X='0'B;
Evaluating y with <a> with 0 and <b> with 0
Procedure A called. Procedure B called.
Y='0'B;
PowerShell
PowerShell handles this natively.
# Simulated fast function
function a ( [boolean]$J ) { return $J }
# Simulated slow function
function b ( [boolean]$J ) { Sleep -Seconds 2; return $J }
# These all short-circuit and do not evaluate the right hand function
( a $True ) -or ( b $False )
( a $True ) -or ( b $True )
( a $False ) -and ( b $False )
( a $False ) -and ( b $True )
# Measure of execution time
Measure-Command {
( a $True ) -or ( b $False )
( a $True ) -or ( b $True )
( a $False ) -and ( b $False )
( a $False ) -and ( b $True )
} | Select TotalMilliseconds
# These all appropriately do evaluate the right hand function
( a $False ) -or ( b $False )
( a $False ) -or ( b $True )
( a $True ) -and ( b $False )
( a $True ) -and ( b $True )
# Measure of execution time
Measure-Command {
( a $False ) -or ( b $False )
( a $False ) -or ( b $True )
( a $True ) -and ( b $False )
( a $True ) -and ( b $True )
} | Select TotalMilliseconds
{{out}}
True
True
False
False
TotalMilliseconds
-----------------
15.653
False
True
False
True
8012.9405
Prolog
Prolog has not functions but predicats succeed of fail. Tested with SWI-Prolog. Should work with other dialects.
short_circuit :-
( a_or_b(true, true) -> writeln('==> true'); writeln('==> false')) , nl,
( a_or_b(true, false)-> writeln('==> true'); writeln('==> false')) , nl,
( a_or_b(false, true)-> writeln('==> true'); writeln('==> false')) , nl,
( a_or_b(false, false)-> writeln('==> true'); writeln('==> false')) , nl,
( a_and_b(true, true)-> writeln('==> true'); writeln('==> false')) , nl,
( a_and_b(true, false)-> writeln('==> true'); writeln('==> false')) , nl,
( a_and_b(false, true)-> writeln('==> true'); writeln('==> false')) , nl,
( a_and_b(false, false)-> writeln('==> true'); writeln('==> false')) .
a_and_b(X, Y) :-
format('a(~w) and b(~w)~n', [X, Y]),
( a(X), b(Y)).
a_or_b(X, Y) :-
format('a(~w) or b(~w)~n', [X, Y]),
( a(X); b(Y)).
a(X) :-
format('a(~w)~n', [X]),
X.
b(X) :-
format('b(~w)~n', [X]),
X.
{{out}}
?- short_circuit.
a(true) or b(true)
a(true)
==> true
a(true) or b(false)
a(true)
==> true
a(false) or b(true)
a(false)
b(true)
==> true
a(false) or b(false)
a(false)
b(false)
==> false
a(true) and b(true)
a(true)
b(true)
==> true
a(true) and b(false)
a(true)
b(false)
==> false
a(false) and b(true)
a(false)
==> false
a(false) and b(false)
a(false)
==> false
true.
PureBasic
Logical '''And''' & '''Or''' operators will not evaluate their right-hand expression if the outcome can be determined from the value of the left-hand expression.
Procedure a(arg)
PrintN(" # Called function a("+Str(arg)+")")
ProcedureReturn arg
EndProcedure
Procedure b(arg)
PrintN(" # Called function b("+Str(arg)+")")
ProcedureReturn arg
EndProcedure
OpenConsole()
For a=#False To #True
For b=#False To #True
PrintN(#CRLF$+"Calculating: x = a("+Str(a)+") And b("+Str(b)+")")
x= a(a) And b(b)
PrintN("Calculating: x = a("+Str(a)+") Or b("+Str(b)+")")
y= a(a) Or b(b)
Next
Next
Input()
{{out}}
Calculating: x = a(0) And b(0)
# Called function a(0)
Calculating: x = a(0) Or b(0)
# Called function a(0)
# Called function b(0)
Calculating: x = a(0) And b(1)
# Called function a(0)
Calculating: x = a(0) Or b(1)
# Called function a(0)
# Called function b(1)
Calculating: x = a(1) And b(0)
# Called function a(1)
# Called function b(0)
Calculating: x = a(1) Or b(0)
# Called function a(1)
Calculating: x = a(1) And b(1)
# Called function a(1)
# Called function b(1)
Calculating: x = a(1) Or b(1)
# Called function a(1)
Python
Pythons '''and''' and '''or''' binary, infix, boolean operators will not evaluate their right-hand expression if the outcome can be determined from the value of the left-hand expression.
def a(answer):
print(" # Called function a(%r) -> %r" % (answer, answer))
return answer
>>> def b(answer):
print(" # Called function b(%r) -> %r" % (answer, answer))
return answer
>>> for i in (False, True):
for j in (False, True):
print ("\nCalculating: x = a(i) and b(j)")
x = a(i) and b(j)
print ("Calculating: y = a(i) or b(j)")
y = a(i) or b(j)
Calculating: x = a(i) and b(j)
# Called function a(False) -> False
Calculating: y = a(i) or b(j)
# Called function a(False) -> False
# Called function b(False) -> False
Calculating: x = a(i) and b(j)
# Called function a(False) -> False
Calculating: y = a(i) or b(j)
# Called function a(False) -> False
# Called function b(True) -> True
Calculating: x = a(i) and b(j)
# Called function a(True) -> True
# Called function b(False) -> False
Calculating: y = a(i) or b(j)
# Called function a(True) -> True
Calculating: x = a(i) and b(j)
# Called function a(True) -> True
# Called function b(True) -> True
Calculating: y = a(i) or b(j)
# Called function a(True) -> True
Pythons if ''expression'' can also be used to the same ends (but probably should not):
for i in (False, True):
for j in (False, True):
print ("\nCalculating: x = a(i) and b(j) using x = b(j) if a(i) else False")
x = b(j) if a(i) else False
print ("Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True")
y = b(j) if not a(i) else True
Calculating: x = a(i) and b(j) using x = b(j) if a(i) else False
# Called function a(False) -> False
Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True
# Called function a(False) -> False
# Called function b(False) -> False
Calculating: x = a(i) and b(j) using x = b(j) if a(i) else False
# Called function a(False) -> False
Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True
# Called function a(False) -> False
# Called function b(True) -> True
Calculating: x = a(i) and b(j) using x = b(j) if a(i) else False
# Called function a(True) -> True
# Called function b(False) -> False
Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True
# Called function a(True) -> True
Calculating: x = a(i) and b(j) using x = b(j) if a(i) else False
# Called function a(True) -> True
# Called function b(True) -> True
Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True
# Called function a(True) -> True
R
The builtins
a <- function(x) {cat("a called\n"); x}
b <- function(x) {cat("b called\n"); x}
tests <- expand.grid(op=list(quote(`||`), quote(`&&`)), x=c(1,0), y=c(1,0))
invisible(apply(tests, 1, function(row) {
call <- substitute(op(a(x),b(y)), row)
cat(deparse(call), "->", eval(call), "\n\n")
}))
{{out}}
a called
a(1) || b(1) -> TRUE
a called
b called
a(1) && b(1) -> TRUE
a called
b called
a(0) || b(1) -> TRUE
a called
a(0) && b(1) -> FALSE
a called
a(1) || b(0) -> TRUE
a called
b called
a(1) && b(0) -> FALSE
a called
b called
a(0) || b(0) -> FALSE
a called
a(0) && b(0) -> FALSE
Because R waits until function arguments are needed before evaluating them, user-defined functions can also short circuit.
switchop <- function(s, x, y) {
if(s < 0) x || y
else if (s > 0) x && y
else xor(x, y)
}
{{out}}
switchop(-1, a(1), b(1))
a called
[1] TRUE
> switchop(1, a(1), b(1))
a called
b called
[1] TRUE
> switchop(1, a(0), b(1))
a called
[1] FALSE
> switchop(0, a(0), b(1))
a called
b called
[1] TRUE
Racket
#lang racket
(define (a x)
(display (~a "a:" x " "))
x)
(define (b x)
(display (~a "b:" x " "))
x)
(for* ([x '(#t #f)]
[y '(#t #f)])
(displayln `(and (a ,x) (b ,y)))
(and (a x) (b y))
(newline)
(displayln `(or (a ,x) (b ,y)))
(or (a x) (b y))
(newline))
{{out}}
(and (a #t) (b #t))
a:#t b:#t
(or (a #t) (b #t))
a:#t
(and (a #t) (b #f))
a:#t b:#f
(or (a #t) (b #f))
a:#t
(and (a #f) (b #t))
a:#f
(or (a #f) (b #t))
a:#f b:#t
(and (a #f) (b #f))
a:#f
(or (a #f) (b #f))
a:#f b:#f
REXX
The REXX language doesn't have native short circuits (it's specifically mentioned in the language specifications that short-circuiting is '''not''' supported).
/*REXX programs demonstrates short-circuit evaluation testing (in an IF statement).*/
parse arg LO HI . /*obtain optional arguments from he CL.*/
if LO=='' | LO=="," then LO= -2 /*Not specified? Then use the default.*/
if HI=='' | HI=="," then HI= 2 /* " " " " " " */
do j=LO to HI /*process from the low to the high.*/
x=a(j) & b(j) /*compute function A and function B */
y=a(j) | b(j) /* " " " or " " */
if \y then y=b(j) /* " " B (for negation).*/
say copies('═', 30) ' x=' || x ' y='y ' j='j
say
end /*j*/
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
a: say ' A entered with:' arg(1); return abs( arg(1) // 2) /*1=odd, 0=even */
b: say ' B entered with:' arg(1); return arg(1) < 0 /*1=neg, 0=if not*/
'''output''' when using the default inputs:
B entered with: -2
A entered with: -2
B entered with: -2
A entered with: -2
══════════════════════════════ x=0 y=1 j=-2
B entered with: -1
A entered with: -1
B entered with: -1
A entered with: -1
══════════════════════════════ x=1 y=1 j=-1
B entered with: 0
A entered with: 0
B entered with: 0
A entered with: 0
B entered with: 0
══════════════════════════════ x=0 y=0 j=0
B entered with: 1
A entered with: 1
B entered with: 1
A entered with: 1
══════════════════════════════ x=0 y=1 j=1
B entered with: 2
A entered with: 2
B entered with: 2
A entered with: 2
B entered with: 2
══════════════════════════════ x=0 y=0 j=2
Ring
# Project : Short-circuit evaluation
for k = 1 to 2
word = ["AND","OR"]
see "
### ===
" + word[k] + "
### ========
" + nl
for i = 0 to 1
for j = 0 to 1
see "a(" + i + ") " + word[k] +" b(" + j + ")" + nl
res =a(i)
if word[k] = "AND" and res != 0
res = b(j)
ok
if word[k] = "OR" and res = 0
res = b(j)
ok
next
next
next
func a(t)
see char(9) + "calls func a" + nl
a = t
return a
func b(t)
see char(9) + "calls func b" + nl
b = t
return b
Output:
### ====== AND ===========
a(0) AND b(0)
calls func a
a(0) AND b(1)
calls func a
a(1) AND b(0)
calls func a
calls func b
a(1) AND b(1)
calls func a
calls func b
### ====== OR ===========
a(0) OR b(0)
calls func a
calls func b
a(0) OR b(1)
calls func a
calls func b
a(1) OR b(0)
calls func a
a(1) OR b(1)
calls func a
Ruby
Binary operators are short-circuiting. Demonstration code:
def a( bool )
puts "a( #{bool} ) called"
bool
end
def b( bool )
puts "b( #{bool} ) called"
bool
end
[true, false].each do |a_val|
[true, false].each do |b_val|
puts "a( #{a_val} ) and b( #{b_val} ) is #{a( a_val ) and b( b_val )}."
puts
puts "a( #{a_val} ) or b( #{b_val} ) is #{a( a_val) or b( b_val )}."
puts
end
end
{{out}}
a( true ) called
b( true ) called
a( true ) and b( true ) is true.
a( true ) called
a( true ) or b( true ) is true.
a( true ) called
b( false ) called
a( true ) and b( false ) is false.
a( true ) called
a( true ) or b( false ) is true.
a( false ) called
a( false ) and b( true ) is false.
a( false ) called
b( true ) called
a( false ) or b( true ) is true.
a( false ) called
a( false ) and b( false ) is false.
a( false ) called
b( false ) called
a( false ) or b( false ) is false.
Run BASIC
for k = 1 to 2
ao$ = word$("AND,OR",k,",")
print "
### ===
";ao$;"
### ========
"
for i = 0 to 1
for j = 0 to 1
print "a("; i; ") ";ao$;" b("; j; ")"
res =a(i) 'call always
'print res;"<===="
if ao$ = "AND" and res <> 0 then res = b(j)
if ao$ = "OR" and res = 0 then res = b(j)
next
next
next k
end
function a( t)
print chr$(9);"calls func a"
a = t
end function
function b( t)
print chr$(9);"calls func b"
b = t
end function
### ====== AND ===========
a(0) AND b(0)
calls func a
a(0) AND b(1)
calls func a
a(1) AND b(0)
calls func a
calls func b
a(1) AND b(1)
calls func a
calls func b
### ====== OR ===========
a(0) OR b(0)
calls func a
calls func b
a(0) OR b(1)
calls func a
calls func b
a(1) OR b(0)
calls func a
a(1) OR b(1)
calls func a
Rust
fn a(foo: bool) -> bool {
println!("a");
foo
}
fn b(foo: bool) -> bool {
println!("b");
foo
}
fn main() {
for i in vec![true, false] {
for j in vec![true, false] {
println!("{} and {} == {}", i, j, a(i) && b(j));
println!("{} or {} == {}", i, j, a(i) || b(j));
println!();
}
}
}
{{out}}
a
b
true and true == true
a
true or true == true
a
b
true and false == false
a
true or false == true
a
false and true == false
a
b
false or true == true
a
false and false == false
a
b
false or false == false
Sather
class MAIN is
a(v:BOOL):BOOL is
#OUT + "executing a\n";
return v;
end;
b(v:BOOL):BOOL is
#OUT + "executing b\n";
return v;
end;
main is
x:BOOL;
x := a(false) and b(true);
#OUT + "F and T = " + x + "\n\n";
x := a(true) or b(true);
#OUT + "T or T = " + x + "\n\n";
x := a(true) and b(false);
#OUT + "T and T = " + x + "\n\n";
x := a(false) or b(true);
#OUT + "F or T = " + x + "\n\n";
end;
end;
Scala
object ShortCircuit {
def a(b:Boolean)={print("Called A=%5b".format(b));b}
def b(b:Boolean)={print(" -> B=%5b".format(b));b}
def main(args: Array[String]): Unit = {
val boolVals=List(false,true)
for(aa<-boolVals; bb<-boolVals){
print("\nTesting A=%5b AND B=%5b -> ".format(aa, bb))
a(aa) && b(bb)
}
for(aa<-boolVals; bb<-boolVals){
print("\nTesting A=%5b OR B=%5b -> ".format(aa, bb))
a(aa) || b(bb)
}
println
}
}
{{out}}
Testing A=false AND B=false -> Called A=false
Testing A=false AND B= true -> Called A=false
Testing A= true AND B=false -> Called A= true -> B=false
Testing A= true AND B= true -> Called A= true -> B= true
Testing A=false OR B=false -> Called A=false -> B=false
Testing A=false OR B= true -> Called A=false -> B= true
Testing A= true OR B=false -> Called A= true
Testing A= true OR B= true -> Called A= true
Scheme
(define (a x)
(display "a\n")
x)
>(define (b x)
(display "b\n")
x)
>(for-each (lambda (i)
(for-each (lambda (j)
(display i) (display " and ") (display j) (newline)
(and (a i) (b j))
(display i) (display " or ") (display j) (newline)
(or (a i) (b j))
) '(#t #f))
) '(#t #f))
#t and #t
a
b
#t or #t
a
#t and #f
a
b
#t or #f
a
#f and #t
a
#f or #t
a
b
#f and #f
a
#f or #f
a
b
Seed7
$ include "seed7_05.s7i";
const func boolean: a (in boolean: aBool) is func
result
var boolean: result is FALSE;
begin
writeln("a");
result := aBool;
end func;
const func boolean: b (in boolean: aBool) is func
result
var boolean: result is FALSE;
begin
writeln("b");
result := aBool;
end func;
const proc: test (in boolean: param1, in boolean: param2) is func
begin
writeln(param1 <& " and " <& param2 <& " = " <& a(param1) and b(param2));
writeln(param1 <& " or " <& param2 <& " = " <& a(param1) or b(param2));
end func;
const proc: main is func
begin
test(FALSE, FALSE);
test(FALSE, TRUE);
test(TRUE, FALSE);
test(TRUE, TRUE);
end func;
{{out}}
a
FALSE and FALSE = FALSE
a
b
FALSE or FALSE = FALSE
a
FALSE and TRUE = FALSE
a
b
FALSE or TRUE = TRUE
a
b
TRUE and FALSE = FALSE
a
TRUE or FALSE = TRUE
a
b
TRUE and TRUE = TRUE
a
TRUE or TRUE = TRUE
Sidef
func a(bool) { print 'A'; return bool }
func b(bool) { print 'B'; return bool }
# Test-driver
func test() {
for op in ['&&', '||'] {
for x,y in [[1,1],[1,0],[0,1],[0,0]] {
"a(%s) %s b(%s): ".printf(x, op, y)
eval "a(Bool(x)) #{op} b(Bool(y))"
print "\n"
}
}
}
# Test and display
test()
{{out}}
a(1) && b(1): AB
a(1) && b(0): AB
a(0) && b(1): A
a(0) && b(0): A
a(1) || b(1): A
a(1) || b(0): A
a(0) || b(1): AB
a(0) || b(0): AB
Simula
BEGIN
BOOLEAN PROCEDURE A(BOOL); BOOLEAN BOOL;
BEGIN OUTCHAR('A'); A := BOOL;
END A;
BOOLEAN PROCEDURE B(BOOL); BOOLEAN BOOL;
BEGIN OUTCHAR('B'); B := BOOL;
END B;
PROCEDURE OUTBOOL(BOOL); BOOLEAN BOOL;
OUTCHAR(IF BOOL THEN 'T' ELSE 'F');
PROCEDURE TEST;
BEGIN
PROCEDURE ANDTEST;
BEGIN
BOOLEAN X, Y, Z;
FOR X := TRUE, FALSE DO
FOR Y := TRUE, FALSE DO
BEGIN
OUTTEXT("A("); OUTBOOL(X);
OUTTEXT(") AND ");
OUTTEXT("B("); OUTBOOL(Y);
OUTTEXT("): ");
Z := A(X) AND THEN B(Y);
OUTIMAGE;
END;
END ANDTEST;
PROCEDURE ORTEST;
BEGIN
BOOLEAN X, Y, Z;
FOR X := TRUE, FALSE DO
FOR Y := TRUE, FALSE DO
BEGIN
OUTTEXT("A("); OUTBOOL(X);
OUTTEXT(") OR ");
OUTTEXT("B("); OUTBOOL(Y);
OUTTEXT("): ");
Z := A(X) OR ELSE B(Y);
OUTIMAGE;
END;
END ORTEST;
ANDTEST;
ORTEST;
END TEST;
TEST;
END.
{{out}}
A(T) AND B(T): AB
A(T) AND B(F): AB
A(F) AND B(T): A
A(F) AND B(F): A
A(T) OR B(T): A
A(T) OR B(F): A
A(F) OR B(T): AB
A(F) OR B(F): AB
Smalltalk
{{works with|GNU Smalltalk}}
The and: or: selectors are shortcircuit selectors but in order to avoid evaluation of the second operand, it must be a block: a and: [ code ] will evaluate the code only if a is true. On the other hand, a and: b, where b is an expression (not a block), behaves like the non-shortcircuit and (&). (Same speech for or |)
Smalltalk at: #a put: nil.
Smalltalk at: #b put: nil.
a := [:x| 'executing a' displayNl. x].
b := [:x| 'executing b' displayNl. x].
('false and false = %1' %
{ (a value: false) and: [ b value: false ] })
displayNl.
('true or false = %1' %
{ (a value: true) or: [ b value: false ] })
displayNl.
('false or true = %1' %
{ (a value: false) or: [ b value: true ] })
displayNl.
('true and false = %1' %
{ (a value: true) and: [ b value: false ] })
displayNl.
SNOBOL4
Because of its unique success/failure model of flow control, Snobol does not use standard boolean operators or assignment. However, in &fullscan mode Snobol exhibits short-circuit boolean behavior in pattern matches, with concatenation " " functioning as logical AND, and alternation " | " as logical OR.
The test statements below use a pattern constructed from the functions a( ) and b( ) and match it to the null string with deferred evaluation. This idiom allows the functions to self-report the expected short-circuit patterns.
define('a(val)') :(a_end)
a out = 'A '
eq(val,1) :s(return)f(freturn)
a_end
define('b(val)') :(b_end)
b out = 'B '
eq(val,1) :s(return)f(freturn)
b_end
* # Test and display
&fullscan = 1
output(.out,1,'-[-r1]') ;* Macro Spitbol
* output(.out,1,'B','-') ;* CSnobol
define('nl()'):(nlx);nl output = :(return);nlx
out = 'T and T: '; null ? *a(1) *b(1); nl()
out = 'T and F: '; null ? *a(1) *b(0); nl()
out = 'F and T: '; null ? *a(0) *b(1); nl()
out = 'F and F: '; null ? *a(0) *b(0); nl()
output =
out = 'T or T: '; null ? *a(1) | *b(1); nl()
out = 'T or F: '; null ? *a(1) | *b(0); nl()
out = 'F or T: '; null ? *a(0) | *b(1); nl()
out = 'F or F: '; null ? *a(0) | *b(0); nl()
end
{{out}}
T and T: A B
T and F: A B
F and T: A
F and F: A
T or T: A
T or F: A
F or T: A B
F or F: A B
Standard ML
{{trans|OCaml}}
fun a r = ( print " > function a called\n"; r )
fun b r = ( print " > function b called\n"; r )
fun test_and b1 b2 = (
print ("# testing (" ^ Bool.toString b1 ^ " andalso " ^ Bool.toString b2 ^ ")\n");
ignore (a b1 andalso b b2) )
fun test_or b1 b2 = (
print ("# testing (" ^ Bool.toString b1 ^ " orelse " ^ Bool.toString b2 ^ ")\n");
ignore (a b1 orelse b b2) )
fun test_this test = (
test true true;
test true false;
test false true;
test false false )
;
print "
### = Testing and =
\n";
test_this test_and;
print "
### = Testing or =
\n";
test_this test_or;
{{out}}
= Testing and =
testing (true andalso true)
function a called function b called
testing (true andalso false)
function a called function b called
testing (false andalso true)
function a called
testing (false andalso false)
function a called
= Testing or =
testing (true orelse true)
function a called
testing (true orelse false)
function a called
testing (false orelse true)
function a called function b called
testing (false orelse false)
function a called function b called
Stata
Stata always evaluates both arguments of operators & and |. Here is a solution with '''if''' statements.
function a(x) {
printf(" a")
return(x)
}
function b(x) {
printf(" b")
return(x)
}
function call(i, j) {
printf("and:")
x = a(i)
if (x) {
x = b(j)
}
printf("\nor:")
y = a(i)
if (!y) {
y = b(j)
}
printf("\n")
return((x,y))
}
'''Example'''
: call(0,1)
and: a
or: a b
1 2
+---------+
1 | 0 1 |
+---------+
: call(1,1)
and: a b
or: a
1 2
+---------+
1 | 1 1 |
+---------+
Swift
Short circuit operators are
func a(v: Bool) -> Bool {
print("a")
return v
}
func b(v: Bool) -> Bool {
print("b")
return v
}
func test(i: Bool, j: Bool) {
println("Testing a(\(i)) && b(\(j))")
print("Trace: ")
println("\nResult: \(a(i) && b(j))")
println("Testing a(\(i)) || b(\(j))")
print("Trace: ")
println("\nResult: \(a(i) || b(j))")
println()
}
test(false, false)
test(false, true)
test(true, false)
test(true, true)
{{out}}
Testing a(false) && b(false)
Trace: a
Result: false
Testing a(false) || b(false)
Trace: ab
Result: false
Testing a(false) && b(true)
Trace: a
Result: false
Testing a(false) || b(true)
Trace: ab
Result: true
Testing a(true) && b(false)
Trace: ab
Result: false
Testing a(true) || b(false)
Trace: a
Result: true
Testing a(true) && b(true)
Trace: ab
Result: true
Testing a(true) || b(true)
Trace: a
Result: true
Tcl
The && and || in the expr command support short-circuit evaluation. It is recommended that you always put expressions in braces so that and command or variable substitutions are applied at the right time rather than before the expression is evaluated at all. (Indeed, it is recommended that you do that anyway as unbraced expressions cannot be efficiently compiled.)
package require Tcl 8.5
proc tcl::mathfunc::a boolean {
puts "a($boolean) called"
return $boolean
}
proc tcl::mathfunc::b boolean {
puts "b($boolean) called"
return $boolean
}
foreach i {false true} {
foreach j {false true} {
set x [expr {a($i) && b($j)}]
puts "x = a($i) && b($j) = $x"
set y [expr {a($i) || b($j)}]
puts "y = a($i) || b($j) = $y"
puts ""; # Blank line for clarity
}
}
{{out}}Note that booleans may be written out words or numeric:
a(false) called
x = a(false) && b(false) = 0
a(false) called
b(false) called
y = a(false) || b(false) = 0
a(false) called
x = a(false) && b(true) = 0
a(false) called
b(true) called
y = a(false) || b(true) = 1
a(true) called
b(false) called
x = a(true) && b(false) = 0
a(true) called
y = a(true) || b(false) = 1
a(true) called
b(true) called
x = a(true) && b(true) = 1
a(true) called
y = a(true) || b(true) = 1
TXR
@(define a (x out))
@ (output)
a (@x) called
@ (end)
@ (bind out x)
@(end)
@(define b (x out))
@ (output)
b (@x) called
@ (end)
@ (bind out x)
@(end)
@(define short_circuit_demo (i j))
@ (output)
a(@i) and b(@j):
@ (end)
@ (maybe)
@ (a i "1")
@ (b j "1")
@ (end)
@ (output)
a(@i) or b(@j):
@ (end)
@ (cases)
@ (a i "1")
@ (or)
@ (b j "1")
@ (or)
@ (accept)
@ (end)
@(end)
@(short_circuit_demo "0" "0")
@(short_circuit_demo "0" "1")
@(short_circuit_demo "1" "0")
@(short_circuit_demo "1" "1")
{{out|Run}}
$ txr short-circuit-bool.txr
a(0) and b(0):
a (0) called
a(0) or b(0):
a (0) called
b (0) called
a(0) and b(1):
a (0) called
a(0) or b(1):
a (0) called
b (1) called
a(1) and b(0):
a (1) called
b (0) called
a(1) or b(0):
a (1) called
a(1) and b(1):
a (1) called
b (1) called
a(1) or b(1):
a (1) called
The a and b functions are defined such that the second parameter is intended to be an unbound variable. When the function binds out, that value propagates back to the unbound variable at the call site. But the way calls works in this language allows us to specify a value instead such as "1". So now the directive @(bind out x) performs unification instead: if x doesn't match "1", the function fails, otherwise it succeeds.
So simply by placing two calls consecutively, we get a short circuting conjunction. The second will not execute if the first one fails.
Short-circuiting disjunction is provided by @(cases).
The @(maybe) construct stops failure from propagating from the enclosed subquery. The @(accept) directive will bail out of the closest enclosing anonymous block (the function body) with a success. It prevents the @(cases) from failing the function if neither case is successful.
UNIX Shell
The ''&&'' and ''||'' operators use the exit status of each command. The ''true'' and ''false'' commands convert a string to an exit status; our code ''&& x=true || x=false'' converts an exit status to a string. {{works with|Bourne Shell}}
a() {
echo "Called a $1"
"$1"
}
b() {
echo "Called b $1"
"$1"
}
for i in false true; do
for j in false true; do
a $i && b $j && x=true || x=false
echo " $i && $j is $x"
a $i || b $j && y=true || y=false
echo " $i || $j is $y"
done
done
The output reveals that
Called a false
false && false is false
Called a false
Called b false
false || false is false
Called a false
false && true is false
Called a false
Called b true
false || true is true
Called a true
Called b false
true && false is false
Called a true
true || false is true
Called a true
Called b true
true && true is true
Called a true
true || true is true
=
C Shell
= Between commands, ''&&'' and ''||'' have short-circuit evaluation. (The aliases for ''a'' and ''b'' must expand to a single command; these aliases expand to an ''eval'' command.)
alias a eval \''echo "Called a \!:1"; "\!:1"'\'
alias b eval \''echo "Called b \!:1"; "\!:1"'\'
foreach i (false true)
foreach j (false true)
a $i && b $j && set x=true || set x=false
echo " $i && $j is $x"
a $i || b $j && set x=true || set x=false
echo " $i || $j is $x"
end
end
Inside expressions, ''&&'' and ''||'' can short circuit some commands, but cannot prevent substitutions.
# Succeeds, only prints "ok".
if ( 1 || { echo This command never runs. } ) echo ok
# Fails, aborts shell with "bad: Undefined variable".
if ( 1 || $bad ) echo ok
# Prints "error", then "ok".
if ( 1 || `echo error >/dev/stderr` ) echo ok
VBA
Private Function a(i As Variant) As Boolean
Debug.Print "a: "; i = 1,
a = i
End Function
Private Function b(j As Variant) As Boolean
Debug.Print "b: "; j = 1;
b = j
End Function
Public Sub short_circuit()
Dim x As Boolean, y As Boolean
'Dim p As Boolean, q As Boolean
Debug.Print "
### ==AND==
" & vbCrLf
For p = 0 To 1
For q = 0 To 1
If a(p) Then
x = b(q)
End If
Debug.Print " = x"
Next q
Debug.Print
Next p
Debug.Print "
### ===OR==
" & vbCrLf
For p = 0 To 1
For q = 0 To 1
If Not a(p) Then
x = b(q)
End If
Debug.Print " = x"
Next q
Debug.Print
Next p
Debug.Print
End Sub
{{out}}
### ==AND==
a: Onwaar = x
a: Onwaar = x
a: Waar b: Onwaar = x
a: Waar b: Waar = x
### ===OR==
a: Onwaar b: Onwaar = x
a: Onwaar b: Waar = x
a: Waar = x
a: Waar = x
Visual Basic .NET
{{trans|c++}}
Module Module1
Function A(v As Boolean) As Boolean
Console.WriteLine("a")
Return v
End Function
Function B(v As Boolean) As Boolean
Console.WriteLine("b")
Return v
End Function
Sub Test(i As Boolean, j As Boolean)
Console.WriteLine("{0} and {1} = {2} (eager evaluation)", i, j, A(i) And B(j))
Console.WriteLine("{0} or {1} = {2} (eager evaluation)", i, j, A(i) Or B(j))
Console.WriteLine("{0} and {1} = {2} (lazy evaluation)", i, j, A(i) AndAlso B(j))
Console.WriteLine("{0} or {1} = {2} (lazy evaluation)", i, j, A(i) OrElse B(j))
Console.WriteLine()
End Sub
Sub Main()
Test(False, False)
Test(False, True)
Test(True, False)
Test(True, True)
End Sub
End Module
{{out}}
a
b
False and False = False (eager evaluation)
a
b
False or False = False (eager evaluation)
a
False and False = False (lazy evaluation)
a
b
False or False = False (lazy evaluation)
a
b
False and True = False (eager evaluation)
a
b
False or True = True (eager evaluation)
a
False and True = False (lazy evaluation)
a
b
False or True = True (lazy evaluation)
a
b
True and False = False (eager evaluation)
a
b
True or False = True (eager evaluation)
a
b
True and False = False (lazy evaluation)
a
True or False = True (lazy evaluation)
a
b
True and True = True (eager evaluation)
a
b
True or True = True (eager evaluation)
a
b
True and True = True (lazy evaluation)
a
True or True = True (lazy evaluation)
Visual FoxPro
*!* Visual FoxPro natively supports short circuit evaluation
CLEAR
CREATE CURSOR funceval(arg1 L, arg2 L, operation V(3), result L, calls V(10))
*!* Conjunction
INSERT INTO funceval (arg1, arg2, operation) VALUES (.F., .F., "AND")
REPLACE result WITH (a(arg1) AND b(arg2))
INSERT INTO funceval (arg1, arg2, operation) VALUES (.F., .T., "AND")
REPLACE result WITH (a(arg1) AND b(arg2))
INSERT INTO funceval (arg1, arg2, operation) VALUES (.T., .F., "AND")
REPLACE result WITH (a(arg1) AND b(arg2))
INSERT INTO funceval (arg1, arg2, operation) VALUES (.T., .T., "AND")
REPLACE result WITH (a(arg1) AND b(arg2))
*!* Disjunction
INSERT INTO funceval (arg1, arg2, operation) VALUES (.F., .F., "OR")
REPLACE result WITH (a(arg1) OR b(arg2))
INSERT INTO funceval (arg1, arg2, operation) VALUES (.F., .T., "OR")
REPLACE result WITH (a(arg1) OR b(arg2))
INSERT INTO funceval (arg1, arg2, operation) VALUES (.T., .F., "OR")
REPLACE result WITH (a(arg1) OR b(arg2))
INSERT INTO funceval (arg1, arg2, operation) VALUES (.T., .T., "OR")
REPLACE result WITH (a(arg1) OR b(arg2))
GO TOP
_VFP.DataToClip("funceval", 8, 3)
FUNCTION a(v As Boolean) As Boolean
REPLACE calls WITH "a()"
RETURN v
ENDFUNC
FUNCTION b(v As Boolean) As Boolean
REPLACE calls WITH calls + ", b()"
RETURN v
ENDFUNC
{{out}}
Arg1 Arg2 Operation Result Calls
F F AND F a()
F T AND F a()
T F AND F a(), b()
T T AND T a(), b()
F F OR F a(), b()
F T OR T a(), b()
T F OR T a()
T T OR T a()
zkl
fcn a(b){self.fcn.println(b); b}
fcn b(b){self.fcn.println(b); b}
{{out}}
a(True) or b(True) //-->Fcn(a)True, True
a(False) or b(True) //-->Fcn(a)False, Fcn(b)True, True
a(False) or b(False) //-->Fcn(a)False, Fcn(b)False, False
a(True) and b(True) //-->Fcn(a)True, Fcn(b)True, True
a(True) and b(False) //-->Fcn(a)True, Fcn(b)False, False
a(False) and b(True) //-->Fcn(a)False, False
{{omit from|GUISS}} {{omit from|ZX Spectrum Basic|does not short circuit}}