Re: [Haskell-cafe] Re: Why can't Haskell be faster?

Robin Green wrote:

On Wed, 31 Oct 2007 14:17:13 +0000 Jules Bean wrote:

...

Specifically, clean's uniqueness types allow for a certain kind of zero-copy mutation optimisation which is much harder for a haskell compiler to automatically infer. It's not clear to me that it's actually worth it, but I think that's the point at issue. I can *imagine* algorithms in which copying is actually faster than mutation, if copying gives you better locality.

If you want in-place update in Haskell, you can use the ST monad, or IORefs. Yes, you have to refactor code, but anecdotally, uniqueness types aren't without problems either - you can make one small change and your code no longer satisfies the uniqueness condition.

IORefs don't give you in-place update. They give you mutation, but new values are still allocated in new heap. foo <- newIORef "hi" writeIORef foo "bye" -- "bye" is a new string, allocated in new heap. the only thing that got -- mutated was a pointer. STArrays and certain IO Arrays give you in-place update, though. Jules