unknownValue.purs

-- ok
x1 :: Int
x1 = y
  where
    z = 42
    (y :: Int) = z

-- ok
x2 :: Int
x2 = y
  where
    y = z
    z = 42

-- nok
x3 :: Int
x3 = y
  where
    (y :: Int) = z -- unknown value z
    z = 42