[Haskell-cafe] forall & ST monad

[Kim-Ee Yeoh]

Peter Verswyvelen-2 wrote:
> 
> I'm having trouble understanding the explanation of the meaning of the
> signature of runST at
> http://en.wikibooks.org/wiki/Haskell/Existentially_quantified_types
> 
> 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?
> 

Existential quantification can be discussed without reference to 
runST, and the more I reread the wikibooks link you gave, the 
more I'm convinced the runST section doesn't belong there.

The tenuous connection between them is higher-ranked types.
You can't do much with existential quantification without
invoking them. That one presupposes the other does not
necessitate its converse. Despite its rank-2 type, runST really
doesn't have anything to do with e.q.

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