[groovy2shoes]

Lua has built-in support for coroutines. Python and Ruby have (limited?) support for coroutines via generators/iterators (via the yield statement).

But why not Icon? It has plenty of neat features on its own, such as goal-directed execution (which I've never seen in another language). Plus it has several pretty solid (and free) introductory e-books: http://www.cs.arizona.edu/icon/books.htm

[rmgraham]

I think some people might see Lua has giving more bang for your buck because of its popularity in things like game scripting among other things.