Icon

Icon is a descendant of SNOBOL4 incorporating similar excellent string processing capabilities, built-in hash tables, success/failure based controls, dynamic storage, automatic type casting and coercion of values. Icon added more conventional procedural syntax, generator expressions, goal-directed evaluation that automatically searches for successful results. String scanning and matching superseded the pattern matching functionality of SNOBOL4.

Several extensions of Icon were developed to improve functionality. Many of these were unified with Unicon

See Also

Merged content

This version of BF takes program and input from the parameter list. Memory grows as needed from a single cell. If no program is specified, the hello world program is run.

BF programtext inputtext

#
# bf interpreter
#
procedure main(arglist)

prog := get(arglist)

# test for nested brackets, previous version was deemed incorrect
if \prog == "hello" then
   prog := ">++++++++[<+++++++++>-]<.>>+>+>++>[-]+<[>[->+<<++++>" ||
           "]<<]>.+++++++..+++.>>+++++++.<<<[[-]<[-]>]<+++++++++" ||
           "++++++.>>.+++.------.--------.>>+.>++++."

# default program
/prog := "++++++++++[>+>+++>++++>+++++++>++++++++>+++++++++>++" ||
         "++++++++>+++++++++++>++++++++++++<<<<<<<<<-]>>>>+.>>>" ||
         ">+..<.<++++++++.>>>+.<<+.<<<<++++.<++.>>>+++++++.>>>.+++." ||
         "<+++++++.--------.<<<<<+.<+++.---."

input := get(arglist)
/input := ""

# 1. toss obvious errors

b := 0
prog ? while i := move(1) do {
   case i of {
      "[" : b +:= 1
      "]" : b -:= 1
      }
   if b < 0 then stop("malformed program, unbalanced []")
   }
if b > 0 then stop("malformed program, unbalanced []")

write("Program is well formed.")
write("Program=",image(prog))
write("Ruler  =",image(repl("0123456789",
      *image(prog)/10 + 1)[1:*image(prog)-1]))

# 2. execute

cell := 1
mem  := [0]
nest := 0

prog ? while i := move(1) do {

   case i of {

      # increment the pointer (to point to the next cell to the right)
      ">" :
            if ( cell +:= 1 ) > *mem then
               put(mem, 0)

      # decrement the pointer (to point to the next cell to the left)
      "<" :
            if ( cell -:= 1 ) < 1 then
               runerr(205,cell)

      # increment (increase by one) the byte at the pointer.
      "+" : mem[cell] +:= 1

      # decrement (decrease by one) the byte at the pointer.
      "-" : mem[cell] -:= 1

      # output the value of the byte at the pointer.
      "." : writes(char(mem[cell]))

      # accept one byte of input, storing its value in the byte at the pointer.
      "," : input ?:= ( mem[cell] := move(1), tab(0) )

      # jump forward to the command after the corresponding ]
      # if the byte at the pointer is zero.
      "[" : if mem[cell] = 0 then {
            repeat {
               i := move(1)
               if i == "[" then nest +:= 1 & next
               if i == "]" then if nest = 0 then break else nest -:= 1
               }
            }

      # jump back to the command after the corresponding [
      # if the byte at the pointer is nonzero.
      "]" : if mem[cell] ~= 0 then {
            move(-1)
            repeat {
               i := move(-1)
               if i == "]" then nest +:= 1 & next
               if i == "[" then if nest = 0 then break else nest -:= 1
               }
            move(1)
            }
      }
      # everything else is ignored/comment
   }
end

Sample output:

#BF
Program is well formed.
Program="++++++++++[>+>+++>++++>+++++++>++++++++>+++++++++>++++++++++>+++++++++++>++++++++++++<<<<<<<<<-]>>>>+.>>>>+..<.<++++++++.>>>+.<<+.<<<<++++.<++.>>>+++++++.>>>.+++.<+++++++.--------.<<<<<+.<+++.---."
Ruler  ="0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345"
Goodbye, World!

#BF hello
Program is well formed.
Program=">++++++++[<+++++++++>-]<.>>+>+>++>[-]+<[>[->+<<++++>]<<]>.+++++++..+++.>>+++++++.<<<[[-]<[-]>]<+++++++++++++++.>>.+++.------.--------.>>+.>++++."
Ruler  ="012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123"
Hello World!

Tasks