Re: [Haskell-cafe] and from standard Prelude

[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

Is there any reason for that besides some clever optimizations?


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?

--
Live well,
~wren
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