[Haskell-cafe] Trouble with the ST monad
andre at digirati.com.br
Mon Dec 29 15:43:56 EST 2008
On Mon, 2008-12-29 at 14:19 -0500, Ross Mellgren wrote:
> The problem is that you're trying to take a STMatrix from some other
> ST computation and freeze it in a new ST computation. The isolation
> between separate computations is done via the rank-2 type variable "s"
> in all those ST functions.
I guess I should go and read the rank-n types page on the wiki...
> Try this:
> freezeMatrix :: (forall s . STMatrix s a) -> Matrix a
> freezeMatrix f :: runST (freezeMatrix f)
Do you know why point-free style doesn't work here even with the type
> Also, instead of using an array of arrays, maybe an array with (Int,
> Int) as the Ix might be a bit smoother?
Thanks for the suggestion. It didn't occur to me that there was an Ix
instance for that.
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