foo :: a -> a
foo x = let x = x in x
foo x = let x = z where z = 2 in x
foo x = let x = z where { z = 2; }; a = 3 in x
foo x = let {g :: Int -> Int; g = id} in ()
let a = b; c = do { foo; bar }; d = baz in b
let a = case True of { True -> foo; False -> bar }; b = foo a in b
foo x = let {?g = id; ?f = g} in x