[Haskell-cafe] How to use STArray?

Udo Stenzel u.stenzel at web.de
Mon Aug 29 19:57:38 EDT 2005

Benjamin Franksen wrote:
> > append :: (IArray UArray e, MArray (STUArray s) e (ST s)) => ...

I believe there must be an MArray instance for every s for this to work.
If I understand types correctly (which isn't all that certain), the
correct context would be

> > append :: (IArray UArray e, forall s . MArray (STUArray s) e (ST s)) => ...

which is illegal.  A workaround might be possible by introducing a new
class which doesn't need to mention s in the context.  I can't see the
solution, though.

Uncle Ed's Rule of Thumb:
        Never use your thumb for a rule.
	You'll either hit it with a hammer or get a splinter in it.
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