#855: Improvements to SpecConstr -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: task | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 6.4.2 Resolution: | Keywords: SpecConstr Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: N/A Blocked By: | Blocking: 915 Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Another way of thinking about: thing in terms of defunctionalisation. Consider this higher order function {{{ let f :: (Int -> Bool) -> Int -> Char f g x = ....(g e)... in ...(f (\x.y+x)).... (f (\v.v*p*q))....(f h)... }}} Now defunctionalise by making a version of `f` that takes a data structure as its argument: {{{ data G_Fun = G1 Int -- \x.y+x | G2 Int Int -- \v.v*p*q | G3 (Int->Int) -- Escape hatch applyG :: G_Fun -> Int -> Bool applyG (G1 x) = \x.y+x applyG (G2 p q) = \v.v*p*q in ...(g e)... applyG (G3 g) = g let f' :: G_Fun -> Int -> Char f' ga x = ...(applyG ga e)... in ...(f' (G1 x))...(f' (G2 p q))...(f' (G3 h)) }}} (I guess you could do this via a w/w kind of transformation, but for now it's purely hypothetical.) Now we are back in the land of data-constructors, where `SpecConstr` thrives. Suppose the call is actually {{{ ...(f' (G1 (Yield e1 e2 e3)))... }}} Should we specialise on `(G1 x)` or on the deeper pattern `(G1 (Yield a b c))`? It depends how much `f'` scrutinises its argument. And you can see that from what `applyG` does. I think you could follow all this reasoning without ''actually'' createing `G_Fun` etc. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/855#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler