unison/unison-src/tests/fix1640.u

unique type Color = Red | Black
unique type RBTree a = Leaf | Tree Color (RBTree a) a (RBTree a)

-- interesting, this typechecks fine
isRed = cases
  Color.Red -> true
  Color.Black -> false

-- as does this 
RBTree.isRed1 = cases
  RBTree.Tree _ _ _ _ -> true
  _ -> false

-- but this did not (before this fix)
RBTree.isRed = cases
  RBTree.Tree Color.Red _ _ _ -> true
  _ -> false

-- In fixing this bug, I noticed that the parser would previously reject
-- this perfectly cromulent pattern match, so I fixed that too.
thisIsTotallyLegit = cases
  [RBTree.Tree _ _ _ _] -> true
  _ -> false