Brainf*ck compiler using C as a midpoint.

compile.js

#!/usr/bin/env node
var fs = require('fs'),
    spawn = require('child_process').spawn,
    argv = require('optimist').argv;

var gcc = spawn('gcc', [
  '--std=c99',
  '-o', argv.o || argv._[0] ? argv._[0].split('.')[0] : 'a.out',
  '-x', 'c',
  '-'
]);

gcc.stdout.pipe(process.stdout);
gcc.stderr.pipe(process.stderr);

gcc.stdin.write([
  '#include <stdio.h>',
  'int main() {',
  'char m[30000];',
  'char *p=m;',
  'FILE *f = NULL;',
  'char mode = 0;'
].join('\n'));

var writeCode = function(err, code) {
  if (err) {
    gcc.kill();
    throw err;
  }

  var brackets = 0;

  var codes = code.split('').filter(function(char) {
    return '+-><.,[]'.indexOf(char) !== -1;
  }).map(function(ins) {
    switch (ins) {
      case '+': return '(*p)++;';
      case '-': return '(*p)--;';
      case '>': return 'p++;';
      case '<': return 'p--;';
      case '.': return 'fputc(*p, mode ? f : stdout);' + '\n' +
                       'fflush(mode ? f : stdout);';
      case ',': return '*p = fgetc(mode ? f : stdout);';
      case '[': brackets++;
                return 'while (*p) {';
      case ']': brackets--;
                return '}';
      case '!': return 'mode = !mode;'
      case '#': return [
          'if (mode) {',
          'if (f) fclose(f);',
          'f = fopen(p, "rw");',
          '}'
        ].join('\n');
    }
  });

  if (brackets > 0) {
    throw Error("uneven amount of '['s");
  } else if (brackets < 0) {
    throw Error("uneven amount of ']'s");
  }

  gcc.stdin.write(codes.join('\n'));

  gcc.stdin.write('return 0;\n}');
  gcc.stdin.end();
};

if (argv._.length) {
  fs.readFile(argv._[0], {encoding: 'utf8'}, writeCode);
} else {
  var code = '';
  process.stdin.on('data', function(chunk) {
    code += chunk;
  });

  process.stdin.on('end', function() {
    writeCode(null, code);
  });
}