f y@(x:xs) = x:y

g x@3 y = x + y

--main has different type as expected
--main  ::  {a} -> {b : 'Num ('MatVecScalarElem a)} -> {c : 'Num a} -> {d:'Int} -> {e : 'Num a}->'Bool
main :: Bool
main = g 3 1 == 5  -- TODO: (5 :: Int)