GHC and the Lazy Functional State Threads Paper

[Thomas Pasch]

Hello, 

to get a better understanding I tried to get the
code from 'Lazy Functional State Thread' to work.
But I encounter some error messages that I don't
fully understand.

> module Lfs where
> 
> import PrelGHC
> import GlaExts
> import ST
> import qualified MArray
> import qualified Array
> 
> newArr = newSTArray
> readArr = readSTArray
> writeArr = writeSTArray
> -- Error: Ambiguous type variable(s) `ix' in the constraint `Ix ix'   
> freezeArr = freezeSTArray 
> 
> thenST_ a b = a `thenST` \_ -> b
> 
> accumArray bnds f z ivs 
>     = runST
>       (newArr bnds z `thenST` \a ->
>        fill a f ivs `thenST_`
>        freezeArr a)
> 
> fill a f [] = returnST ()
> fill a f ((i,v):ivs)
>      = readArr a i `thenST` \x ->
>        writeArr a i (f x v) `thenST_`
>        fill a f ivs
> 
> -- in GlaExts: seqST = (>>) 
> seqST2 = foldr thenST_ (returnST ())
> 
> accumArray2 bnds f z ivs 
>     = runST 
>       (newArr bnds z `thenST` \a ->
>        seqST2 (map (update a f) ivs) `thenST_`
>        freezeArr a)
> 
> update a f (i,v) 
>     = readArr a i `thenST` \x ->
>       writeArr a i (f x v)
> 
> putString [] = returnST ()
> --  Error: Couldn't match `ST s a' against `IO ()' 
> putString (c:cs) = putChar c `thenST_`
> 		   putString cs
> 
> -- Error: Couldn't match `ST s a' against `[b]'  
> putString2 cs = seqST (map putChar cs)
> 
> main = putStrLn "Hello, world"
> 

How to change the code to get it to work? Why is
there a different definition of seqST in GlaExts?

Best regards,

Thomas

PS:
When I change the definition of the mutable Array to

> newArr = MArray.newArray
> readArr = MArray.readArray
> writeArr = MArray.writeArray
> freezeArr = MArray.freeze

I get Error in accumArray and accumArray2. I guess
this is because of the fact that a STArray is only 
one possible MArray and there are other possiblities,
right?