Does anyone know what kind of performance you can get out of this? I love the idea of a Haskell->JS compiler, but the YHC JS backend seemed petrifying in terms of efficiency (even though it's cool as hell).

My current project uses Obj-J/Cappuccino extensively and it's working well for me. For my next project I want to play with something else, so far I've looked at:

st2js: nope, hate Squeak

scheme2js: works well but debugging is extremely painful, due to the specific combination of unreadable JS output and that both the source and target language are dynamic. also, I wouldn't use HOP at all, and the GUI/library stuff seemed integrated with it.

Clamato: one to watch, though the last version I played with (when it appeared on HN) made my browsers lag badly

ocamljs: haven't gotten to play with it yet, but this seemed promising. not sure about how it handles partial evaluation/currying, though, it didn't seem too sophisticated when i i looked at it. (let me know if I'm mistaken)

haXe: lots of the features I like, but I loathe C syntax for these kinds of languages.

pyjamas: i like python but not when it's executing in an environment where i'd normally get real lexical scoping and lambdas. :)

also there's obviously GWT, but c'mon, I want to have fun.

any others I'm missing?

For Haskell, there's also this: http://hackage.haskell.org/package/jsmw It's _sort_ of like a JavaScript backend.

Cool, I actually like stuff like this :)