Async Compiler

asyncTest.js

var compiler = require('./asyncCompiler'),
    fs = require('fs');

compiler.helpers = {
  partial: function (filename, data, callback) {
    fs.readFile(filename, function (err, text) {
      if (err) { callback(err); return; }
      compiler(text, data, callback);
    });
  }
}

var template = "Hello @planet, my name is @name() and I am @age() years old.";
var data = {
  // Value
  planet: "world",
  // Async helper
  name: function name(callback) {
    process.nextTick(function () {
      callback(null, "Tim Caswell");
    });
  },
  // Sync helper
  age: function age() {
    return 28;
  }
};

// Get the compiled template, and the execute it
var fn = compiler(template);
console.log("\nJavaScript");
console.log(fn.toString());

fn(data, function (err, text) {
  console.log("OUTPUT " + text);

  // Or do it in one shot
  compiler(template, data, function (err, text) {
    console.log("OUTPUT2 " + text);

    // Or use a stream
    var stream = new process.EventEmitter();
    fn(data, stream);
    stream.addListener('data', function (data) {
      console.log("DATA " + JSON.stringify(data.toString()));
    });
    stream.addListener('end', function () {
      console.log("END");
    });
    stream.addListener('error', function (err) {
      console.log("ERROR " + err.stack);
    });

  });

});

output.txt

JavaScript
function fn(locals, callback) {
  locals.__proto__ = module.exports.helpers;
  var position = 0, stream, chunks;
  if (!(typeof callback === 'function')) {
    if (callback instanceof process.EventEmitter) {
      stream = callback;
      callback = undefined;
    } else {
      throw new Error("Type Error: last argument must be either a callback function or stream instance");
    }
  }
  function check() {
    var pieces = [];
    while (chunks[position] && position < chunks.length) {
      if (stream) {
        pieces.push(chunks[position]);
      }
      position++;
    }
    if (stream && pieces.length > 0) {
      stream.emit('data', new Buffer(pieces.join("")));
    }

    if (position === chunks.length) {
      if (callback) {
        callback(null, new Buffer(chunks.join("")));
      }
      if (stream) {
        stream.emit('end');
      }
    }
  }
  function execute(position, fn) {
    try {
      chunks[position] = fn(function (err, result) {
        if (err) { 
          if (stream) stream.emit('error', err);
          if (callback) callback(err);
          return;
        }
        chunks[position] = result;
        check();
      });
    } catch (err) {
      if (stream) stream.emit('error', err);
      if (callback) callback(err);
    }
  }

  process.nextTick(function () {
    with(locals) {
      // START GENERATED CODE
      chunks = new Array(5);
      chunks[0] = "Hello " + planet + ", my name is ";
      execute(1, name);
      chunks[2] = " and I am ";
      execute(3, age);
      chunks[4] = " years old";
      check();
      // END GENERATED CODE
    }
  });
}
OUTPUT Hello world, my name is Tim Caswell and I am 28 years old
OUTPUT2 Hello world, my name is Tim Caswell and I am 28 years old
DATA "Hello world, my name is "
DATA "Tim Caswell and I am 28 years old"
END

Updated API per bradleymeck's suggestions on IRC