On Wed, Aug 18, 2010 at 9:56 PM, wren ng thornton
Oleg Lobachev wrote:
#ifdef USE_REPORT_PRELUDE and = foldr (&&) True or = foldr (||) False #else and [] = True and (x:xs) = x && and xs or [] = False or (x:xs) = x || or xs
{-# RULES
"and/build" forall (g::forall b.(Bool->b->b)->b->b) . and (build g) = g (&&) True
"or/build" forall (g::forall b.(Bool->b->b)->b->b) . or (build g) = g (||) False
#-} #endif
The thing I find puzzling is that the foldr is inlined. The (regular) clever optimizations for build/foldr seem like they should already handle this without the need for the extra rules. I wonder how much is gained by specializing to (&&)/True instead of relying on the regular deforestation?
The above code does not inline and / or, *unless they are fused using the RULES.* There's not really any benefit to inlining them otherwise, and it duplicates code. -Jan-Willem Maessen
-- Live well, ~wren _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe