testsuite/tests/typecheck/should_fail/T5978.hs

   1 {-# LANGUAGE MultiParamTypeClasses #-}
   2 {-# LANGUAGE FunctionalDependencies #-}
   3 module T5978 where
   4
   5 class C from to | from -> to where
   6
   7 instance C Float Char where
   8 instance C Double Bool where
   9
  10
  11 polyFoo :: (C from to) => from
  12 polyFoo = undefined
  13
  14 polyBar ::
  15    (C fromA toA, C fromB toB) =>
  16    (toA -> toB) ->
  17    fromA -> fromB
  18 polyBar = undefined
  19
  20
  21 monoBar :: Double
  22 monoBar = polyBar id monoFoo
  23 -- fromA = Float, fromB = Double, toA = toB
  24 -- [W] C Float to, C Double to
  25 -- => [D] to ~ Char, [D] to ~ Bool
  26
  27 monoFoo :: Float
  28 monoFoo = polyFoo
  29