testsuite/tests/patsyn/should_fail/T11667.hs

   1 {-# LANGUAGE PatternSynonyms, GADTs #-}
   2 module T11667 where
   3
   4 {-
   5 The following four pattern synonym declarations should give valid
   6 error messages
   7 -}
   8
   9 -- Check if we mention no explicit type signature (or the correct
  10 -- signature "Eq a => Maybe a")
  11 pattern Pat1 :: Eq a => Maybe a
  12 pattern Pat1 <- Just 42
  13
  14 -- Check if we mention no explicit type signature (or the correct
  15 -- signature "forall b. () => forall a. b ~ Bool => a -> b -> (b, T)")
  16 data T where MkT :: a -> T
  17 pattern Pat2 :: () => b ~ Bool => a -> b -> (b, T)
  18 pattern Pat2 x y = (y, MkT x)
  19
  20 -- Check if we do not tell the user that we could not deduce (Show a)
  21 -- from the "required" context. Also, check if we do not give the
  22 -- possible fix that suggests to add (Show a) to the "required" context.
  23 pattern Pat3 :: Eq a => Show a => a -> Maybe a
  24 pattern Pat3 x <- Just x
  25
  26 -- Check if we return a valid error message concerning the missing
  27 -- constraint (Num a) when the bidirectional pattern synonym is used
  28 -- in an expression context
  29 data S a where MkS :: (Num a, Show a) => a -> S a
  30 pattern Pat4 :: (Eq a) => (Show a) => S a
  31 pattern Pat4 = MkS 42