Taylor Skidmore Taylor Skidmore - 4 months ago 28
Brainfuck Question

Brainfuck interpreter in Nimrod

I am currently toying with Nimrod by writing a Brainfuck interpreter in the language. Currently, without loops implemented, I have:

import os, unsigned

const RamSize = 200

type
TRam = array[0..RamSize, int]

var
ram : TRam
ip : int = 0
dp : int = 0

proc readCode(path: string) =
var
f : TFile = open(path)
i : int = 0
while i < RamSize and not EndOfFile(f):
ram[i] = ord(readChar(f))
inc(i)

proc main(path: string) =

readCode(path)
while ip < RamSize:
case chr(ram[ip])
of '>' : inc dp
of '<' : dec dp
of '+' : inc ram[dp]
of '-' : dec ram[dp]
of '.' : write stdout, chr(ram[dp])
else : nil
inc(ip)
echo()

if paramcount() == 1: main(paramstr(1))
else: echo("usage: bfrun PATH")


It compiles successfully, but when I throw an input at it like:

>
+++++ +++++
+++++ +++++
+++++ +++++
+++++ +++++
+++++ +++++
+++++ +++++
+++++ .


Which should print the character 'A' it returns 'N.' Any ideas?

Answer

If I understand this correctly, it looks like dp is set to 1, and then ram[dp] is incremented 65 times. But ram[dp], aka ram[1], starts out holding the second character of the program, which is a carriage return character (ASCII 13). A is ASCII 65, N is ASCII 78, and 65 + 13 is 78.

Set dp to somewhere outside of program space before you start incrementing the memory cell -- or use separate RAM to hold the program.