testsuite/tests/typecheck/should_fail/tcfail149.hs

   1 {-# LANGUAGE ConstrainedClassMethods #-}
   2
   3 module Main where
   4
   5 class C a where
   6   op :: (Show a, Show b) => a -> b -> String
   7         -- This class op adds a constraint on 'a'
   8
   9         -- In GHC 7.0 this is fine, and it's a royal
  10         -- pain to reject it when in H98 mode, so
  11         -- I'm just allowing it
  12
  13 instance C Int where
  14   op x y = show x ++ " " ++ show y
  15
  16 main = print (op (1::Int) 2)