[Haskell] Image manipulation

[Stefan O'Rear]

On Wed, Oct 31, 2007 at 10:58:40AM +0100, Ketil Malde wrote:
> Bjorn Lisper <lisper at it.kth.se> writes:
> 
> > Wait, Jerzy. Haskell implementations do not have to be lazy as long as they
> > preserve the more abstract semantics. Optimistic evaluation has been
> > considered, for instance by Robert Ennals.
> 
> I'm not sure if the GC hack proposed by Wadler¹ that lets the garbage
> collector replace "fst (a,b)" with "a" (and similar for other unchecked
> selectors) counts as optimistic evaluation, but I wonder what the
> status of this is.  GHC doesn't seem to do it, and I wonder if there
> is any particular reason?  Too specific?

GHC nominally does do it (look for 'selector thunks' in the RTS and
commentary), but it doesn't work and we don't know why.

http://hackage.haskell.org/trac/ghc/ticket/1038

Stefan
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