[Haskell-cafe] forall & ST monad
a.biurvOir4 at asuhan.com
Sun Feb 15 14:50:20 EST 2009
Peter Verswyvelen-2 wrote:
> I could try to read the article a couple of times again, but are there any
> other good readings about these existentially quantified types and how the
> ST monad works?
The primary source is if I'm not mistaken, the following
"State in Haskell" paper:
Having said that, I'm not sure about the statement on page 9
that "readVar v simply does not have type forall s. ST s Bool."
The variable v could be of type "forall s. MutVar s Bool",
in which case all of "runST (readVar v)" typechecks.
The sticking point really arises from "runST (newVar True)".
So there isn't really "the other way round", but rather only
Am I misreading something? A minor nit, to be sure.
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