[Haskell-cafe] forall & ST monad

[Peter Verswyvelen]

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?

I'm currently only using forall in combination with type classes, as in data
MVC m v = forall c. Controller c => MVC m v c

However - as the article mentions - forall can also be used to constrain the
scope of type variables, but I don't get it yet.

Thanks!
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