Non-exhaustive patterns in "match" expressions

[tim2CF]

type maybe 'a = Just 'a | Nothing

val (>>=) 'a 'b : fn (maybe 'a) (fn 'a -> maybe 'b) -> (maybe 'b)
let (>>=) x f =
  match x with
    Nothing -> Nothing
    -- | Just y -> f y

This code is compiled without warnings/errors, but it should not (because 2nd clause is commented out)

[lpil]

Only top level expressions have exhaustiveness checking at present -> https://github.com/alpaca-lang/alpaca#using-it

[tim2CF]

@lpil that's fine, but top-level expressions based variant is not compiling (even if patterns are exhaustive)

#269