[Haskell-cafe] Re: Shootout favoring imperative code

[Einar Karttunen]

On 09.01 11:32, Simon Marlow wrote:
> Sebastian Sylvan wrote:
> 
> >It would be neat if the PackedString library contained functions such
> >as hGetLine etc. It does have a function for reading from a buffer,
> >but it won't stop at a newline...
> >But yeah, fast string manipulation is difficult when using a
> >linked-list representation...
> 
> My version of the packed string library does have an hGetLine.  Don 
> Stewart was merging my version with his fps at some point, Don - any 
> news on that?

Getting a fast FastPackedString will solve the problems with many
benchmarks. A similar thing for arrays would be nice - although
this is more about inteface:

> module Data.Array.UnsafeOps where
>
> import Data.Array.Base hiding((!))
>
> {-# INLINE (!) #-}
> (!) :: MArray a e m => a Int e -> Int -> m e
> (!) = unsafeRead
>
> {-# INLINE set #-}
> set :: MArray a e m => a Int e -> Int -> e -> m ()
> set = unsafeWrite
>
> {-# INLINE swap #-}
> swap :: MArray a e m => a Int e -> Int -> Int -> m ()
> swap arr x y = do xv <- arr ! x
>                   yv <- arr ! y
>                   set arr x yv
>                   set arr y xv
>
> {-# INLINE combineTo #-}
> combineTo :: MArray a e m => a Int e -> Int -> (e -> e -> e) -> a Int e -> Int -> m ()
> combineTo a0 i0 f a1 i1 = do v0 <- a0 ! i0
>                              v1 <- a1 ! i1
>                              set a0 i0 $! f v0 v1

and so forth. Usually imperative solutions have something like
"a[i] += b[i]", which currently is quite tedious and ugly to
translate to MArrays. Now it would become "combineTo a i (+) b i".

- Einar Karttunen