Skip to content

case expression with mixed use of Num instances cause spurious overlap warning

newtype Whomp = Whomp Int
  deriving (Eq)

instance Num Whomp where
  Whomp a + Whomp b = Whomp (a+b)
  Whomp a * Whomp b = Whomp (a*b)
  abs (Whomp a) = Whomp (abs a)
  signum (Whomp a) = Whomp (signum a)
  fromInteger = Whomp . fromInteger

foo :: Whomp -> String
foo cc = case cc of
    Whomp 0 -> "zero"
    10 -> "ten"

produces

Foo.hs:12:10: Warning:
    Pattern match(es) are overlapped
    In a case alternative: Whomp 0 -> ...
Trac metadata
Trac field Value
Version 7.6.3
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information