[Haskell-cafe] How to use STArray?

[Udo Stenzel]

Bayley, Alistair wrote:
> compute :: Int -> Int
> compute n = runST ( do
>     arr <- newArray (-1, 1) n
>     readArray 1 arr
>   )

You messed the argument order to readArray up.  Even with that repaired,
you'll need a type signature somewhere to help ghc resolve the
overloading of newArray and readArray, which is surprisingly tricky due
to the "s" that must not escape.  This works:

compute :: Int -> Int
compute n = runST ( do
    arr <- newArray (-1, 1) n :: ST s (STArray s Int Int)
    readArray arr 1
  )



Udo.
-- 
Mikrosoft spel chekar four sail, wurks grate!
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