Document how to write a pattern synonym that uses a view pattern
It took me a bit to figure out how to apply a function to the expression that I want to pattern match on – turns out you can use
ViewPatterns, as for example
pattern (:<|) :: a -> Seq a -> Seq a pattern x :<| xs <- (viewl -> x :< xs) where x :<| xs = x <| xs
I think this should be documented in the user's guide.