transform.js

function transform(transformer, input, buffer) {
  var channel = new Channel(buffer)
  transformer(input, channel.output)
  return channel.input
}

var map = function(input, f, close) {
  return transform(function(input, output) {
    spawn(function*() {
      while (var chunk = yield input.take(), take !== void(0)) {
        yield output.put(f(chunk))
      }
      if (close)
        output.close()
    })
  })
}