coroutine.coffee

$coroutine = (func) -> ->
  gen = func(arguments...)
  gen.next()
  gen

grep = $coroutine (pattern) ->
  console.log "Looking for #{pattern}"
  while true
    line = yield
    if line.indexOf pattern != -1
      console.log "Found #{pattern} in #{line}"
  on

g = grep("Coffee")

g.send("JavaScript")
g.send("CoffeeScript")

Try: line = yield``

Yep, thanks, actually it's OK, just JS 1.7 was disabled. Coffee normally compiles yield as an identifier. Though, if to reserve it as the keyword, it should fail to compile when yield is used improperly.