PrelBase contains the appended code. Am I correct in
assuming that the stuff is structured as it is, because the
"map" rule first `breaks' the map `open', which exposes it
to the various foldr/build rules, and if no foldr/build rule
matches, the "mapList" rule `closes' it again in a later
phase of optimisation - after build was inlined? If so, it
seems like the whole thing depends a bit on the timing of
the various optimsations (the map might be closed again
before any of the foldr/build rules fires). Is this maybe
the reason that build has an INLINE 2 pragma, which delays
its inlining, and thus, the closing of the map?
All very cunning, it seems ;-)
Cheers,
Manuel
-=-
map :: (a -> b) -> [a] -> [b]
map = mapList
-- Note eta expanded
mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
mapFB c f x ys = c (f x) ys
mapList :: (a -> b) -> [a] -> [b]
mapList _ [] = []
mapList f (x:xs) = f x : mapList f xs
{-# RULES
"map" forall f xs. map f xs = build (\c n -> foldr (mapFB
c f) n xs)
"mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
"mapList" forall f. foldr (mapFB (:) f) [] = mapList f
#-}
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