Robin Green wrote:
On Wed, 31 Oct 2007 14:17:13 +0000
Jules Bean <[EMAIL PROTECTED]> 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
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