Hashable instance with tuples

instance Hashable LeafExpr where
    hash (Var name) = hash ("Leaf-Var", name)
    hash Star = hash "Leaf-Star"
    hash (Const n) = hash ("Leaf-Const", n)

instance Hashable UnaryOp where
    hash (Neg) = hash "Unary-Neg"
    hash (BinNot) = hash "Unary-BinNot"

instance Hashable BinaryOp where
    hash (Plus) = hash "Binary-Plus"
    hash (Minus) = hash "Binary-Minus"
    hash (Times) = hash "Binary-Times"
    hash (Div) = hash "Binary-Div"
    hash (Mod) = hash "Binary-Mod"

instance Hashable NodeExpr where
    hash (Leaf node) = hash ("Leaf", node)
    hash (Unary op node) = hash ("Unary", op, node)
    hash (Binary op node node') = hash ("Binary", op, node, node')