Re: Arrays and arrays

ketil@ii.uib.no (Ketil Z. Malde) writes:

Hal Daume III writes:

...

Yes, (//) is terrible. It *never* tries to update in-place.

Any reason it couldn't be done in-place? (I.e. thaw, update all, and freeze again) Am I missing something -- Could partial results be used, the update list be infinite, or anything like that?

I'm toying with STArrays in order to fix this. In prinicple it should be simple, but it ended up a tangled mess of incomprehensible warnings and strange errors. Oh well, I've boiled it down to something like: replace :: UArray Int Int -> [(Int,Int)] -> UArray Int Int replace a p = runST (thaw a >>= \u -> update u p >> freeze u) update :: STUArray () Int Int -> [(Int,Int)] -> ST () () update u ps = mapM_ (uncurry (writeArray u)) ps Which gives me Compiling SuffixArray ( SuffixArray.lhs, interpreted ) SuffixArray.lhs:131: Cannot unify the type-signature variable `s' with the type `()' Expected type: ST s a Inferred type: ST () (b Int Int) In the expression: (thaw a) >>= (\ u -> (update u p) >> (freeze u)) In the first argument of `runST', namely `((thaw a) >>= (\ u -> (update u p) >> (freeze u)))' I've tried rearranging the code in various ways, but I can get no further. Sounds to me that setting s=() and a=(b Int Int) would do the trick, but apparently the compiler disagrees. I haven't used the ST monad before, so perhaps I'm missing something obvious? -kzm -- If I haven't seen further, it is by standing in the footprints of giants