#9701: GADTs not specialized properly -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: Runtime | Blocked By: performance bug | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Description changed by dfeuer: Old description:
This has probably been raised before, but I can't find a ticket. If I write
{{{#!hs data Silly a where Silly :: Ord a => a -> Silly a
isItSilly :: a -> Silly a -> Bool isItSilly a (Silly x) = a < x
isItSillyInt :: Int -> Silly Int -> Bool isItSillyInt = isItSilly }}}
then I get
{{{ isItSilly isItSilly = \ @ a_aBq eta_B2 eta1_B1 -> case eta1_B1 of _ { Silly $dOrd_aBs x_aAy -> < $dOrd_aBs eta_B2 x_aAy }
isItSillyInt isItSillyInt = isItSilly }}}
Although GHC knows that `eta_B2` is an `Int`, and `x_aAy` therefore must be one as well, it looks up the `<` method in the `eta1_B1` dictionary instead of just using `ltInt`.
New description: This has probably been raised before, but I can't find a ticket. If I write {{{#!hs data Silly a where Silly :: Ord a => a -> Silly a isItSilly :: a -> Silly a -> Bool isItSilly a (Silly x) = a < x isItSillyInt :: Int -> Silly Int -> Bool isItSillyInt = isItSilly }}} then I get {{{ isItSilly isItSilly = \ @ a_aBq eta_B2 eta1_B1 -> case eta1_B1 of _ { Silly $dOrd_aBs x_aAy -> < $dOrd_aBs eta_B2 x_aAy } isItSillyInt isItSillyInt = isItSilly }}} Although GHC knows that `eta_B2` and `x_aAy` are `Int`, it looks up the `<` method in the `eta1_B1` dictionary instead of just using `ltInt`. Note: it does not help to `INLINE` `isItSilly`. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9701#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler