Brainfuck interpreter

run=(code, input)->
    [dptr, cptr, marks, mem, output, stack]=[0, 0, [], (0 for [1..100]), [], []]

    for cmd, pos in code
        if cmd is '[' then stack.push(pos)
        if cmd is ']' then marks[marks[pos] = stack.pop()]=pos  
  
    while cptr < code.length
        switch code[cptr]
            when '+' then mem[dptr] = mem[dptr] + 1 or 1
            when '-' then mem[dptr] = mem[dptr] - 1 or 0
            when '>' then dptr++
            when '<' then dptr--
            when '[' then cptr = marks[cptr] if mem[dptr] is 0
            when ']' then cptr = marks[cptr] if mem[dptr] isnt  0
            when '.' then output.push(String.fromCharCode(mem[dptr]))
            when ',' then c=input.shift(); mem[dptr] = c.charCodeAt(0) if c instanceof string
        cptr++
    output