#12708: RFC: Representation polymorphic Num -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Core Libraries | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Using the generalized function composition from the paper {{{#!hs (·) :: forall (r :: RuntimeRep) (a :: Type) (b :: Type) (c :: TYPE r). (b -> c) -> (a -> b) -> (a -> c) (f · g) x = f (g x) }}} we can write {{{#!hs fromInteger :: Integer -> Int# fromInteger (fromInteger -> I# i) = i fromInteger :: Integer -> Int# fromInteger (fromInteger -> D# d) = d) }}} pointfree {{{#!hs fromInteger :: Integer -> Int# fromInteger = getInt# · fromInteger where getInt# :: Int -> Int# getInt# (I# i) = i fromInteger :: Integer -> Double# fromInteger = getDouble# · fromInteger where getDouble# :: Double -> Double# getDouble# (D# d) = d -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12708#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler