_expr :: Parser TypeAST'
type_expr = try type_fun
        <|> try type_app
        <|> try type_var
        <|> parens type_expr

an
type_expr :: Parser TypeAST'
type_expr = try type_fun
        <|> try type_app
        <|> try type_var
        <|> parens type_expr
type_expr = try type_fun
        <|> try type_app
        <|> try type_var
        <|> parens type_expr