interpreter.js

module.exports = function (tokens, state) {
  const length = tokens.length;
  let i = 0;

  while (i < length) {
    const { pointer, tape, } = state;
    const bite = tape[pointer];

    const { character, end, line, start, type, } = tokens[i];

    if (type === '[') {
      if (bite) {
        ++i;
        continue;
      } else {
        i = end + 1;
        continue;
      }
    }

    if (type === ']') {
      if (bite) {
        i = start + 1;
        continue;
      } else {
        ++i;
        continue;
      }
    }

    if (type === '+') {
      const nextBite = (tape[pointer] || 0) + 1;
      state.tape[pointer] = nextBite > 255 ? 0 : nextBite;
    }

    if (type === '-') {
      const nextBite = (tape[pointer] || 0) - 1;
      state.tape[pointer] = nextBite < 0 ? 255 : nextBite;
    }

    if (type === '<') {
      --state.pointer;

      if (state.pointer !== state.pointer || state.pointer < 0) {
        throw new RangeError(
          `Your program used the < command one too many times in a row.
          You are already at the left-most memory position.
          Check line ${line}, character ${character}.`
        );
      }
    }

    if (type === '>') {
      ++state.pointer;
    }

    if (type === ',') {
      state.tape[pointer] = state.input.charCodeAt() || 0;
      state.input = state.input.substring(1);
    }

    if (type === '.') {
      state.output += String.fromCharCode(tape[pointer]);
    }

    ++i;
  }

  return state;
};