Stefan O'Rear wrote:
On Wed, Oct 31, 2007 at 10:58:40AM +0100, Ketil Malde wrote:
Bjorn Lisper <[EMAIL PROTECTED]> 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
GHC HEAD has a fix for the example in that ticket, and 6.8.1 has a
workaround (I bumped the recursion depth limit enough to make it run in
constant space). Do you have an example that still doesn't work,
particularly with the HEAD?
Cheers,
Simon
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