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> procedure main(arglist)

prog := get(arglist) /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",*prog/10)))

1. 2. execute

cell := 1 mem  := [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)

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

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

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

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

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

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

end</lang>

Sample output:

#BF 
Program is well formed.
Program="++++++++++[>+>+++>++++>+++++++>++++++++>+++++++++>++++++++++>+++++++++++>++++++++++++<<<<<<<<<-]>>>>+.>>>>+..<.<++++++++.>>>+.<<+.<<<<++++.<++.>>>+++++++.>>>.+++.<+++++++.--------.<<<<<+.<+++.---."
Ruler  ="0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"
Goodbye, World!