print (EmptyListExpr _) = ["[]"]
print (TupleExpr _ (e1, e2)) = ["(":print e1] ++ [",":print e2] ++ [")"]
instance toString Expr where
print (EmptyListExpr _) = ["[]"]
print (TupleExpr _ (e1, e2)) = ["(":print e1] ++ [",":print e2] ++ [")"]
instance toString Expr where