Execute Brain****/Icon

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

<lang Icon>#

1. bf interpreter

procedure main(arglist)

prog := get(arglist)

1. test for nested brackets, previous version was deemed incorrect

if \prog == "hello" then

  prog := ">++++++++[<+++++++++>-]<.>>+>+>++>[-]+<[>[->+<<++++>" ||
          "]<<]>.+++++++..+++.>>+++++++.<<<[[-]<[-]>]<+++++++++" ||
          "++++++.>>.+++.------.--------.>>+.>++++."

1. default program

/prog := "++++++++++[>+>+++>++++>+++++++>++++++++>+++++++++>++" ||

        "++++++++>+++++++++++>++++++++++++<<<<<<<<<-]>>>>+.>>>" ||
        ">+..<.<++++++++.>>>+.<<+.<<<<++++.<++.>>>+++++++.>>>.+++." ||
        "<+++++++.--------.<<<<<+.<+++.---."

input := get(arglist) /input := ""

1. 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]))

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</lang>

Sample output:

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

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