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I want to write the following record pattern synonym

pattern MkOp :: Op -> Exp -> Exp -> Exp
pattern MkOp {(·), a, b} <- (splitOp -> Just ((·), a, b))
  where MkOp (·) a b      = a · b

given this code

data Exp = Val Int | Add Exp Exp | Mul Exp Exp deriving Show

type Op = Exp -> Exp -> Exp

splitOp :: Exp -> Maybe (Op, Exp, Exp)
splitOp (Add a b) = Just (Add, a, b)
splitOp (Mul a b) = Just (Mul, a, b)
splitOp _         = Nothing

It works fine if (·) is replaced by operator. Fields of regular data types works just fine:

data F a = F {
  (·) :: a -> a -> a, 
  x   :: a, 
  y   :: a
}

f F{(·), x, y} = x·y
g F{..}        = x·y

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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