即使启用了DeriveGeneric，派生Generic也不起作用

本文介绍了即使启用了DeriveGeneric，派生Generic也不起作用的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在尝试遵循Beam Haskell库的教程: tathougies.github.io/beam/tutorials/tutorial1/

I'm trying to follow the tutorial for the Beam Haskell library: tathougies.github.io/beam/tutorials/tutorial1/

module Lib ( someFunc ) where {-# LANGUAGE DeriveGeneric , GADTs , OverloadedStrings , FlexibleContexts , FlexibleInstances , TypeFamilies , TypeApplications #-} import Database.Beam import Database.Beam.Postgres import GHC.Generics import Data.Text (Text) data UserT f = User { _userEmail :: Columnar f Text , _userFirstName :: Columnar f Text , _userLastName :: Columnar f Text , _userPassword :: Columnar f Text } deriving Generic someFunc :: IO () someFunc = putStrLn "someFunc"

这将导致以下错误:

• Can't make a derived instance of ‘Generic (UserT f)’: You need DeriveGeneric to derive an instance for this class • In the data declaration for ‘UserT’ | 27 | deriving Generic | ^^^^^^^

请注意，存在DeriveGeneric语言编译指示.

Note that the DeriveGeneric language pragma is present.

我在这里想念什么?

构建环境:

• 堆叠lts-11.9
• Linux

推荐答案

{-# LANGUAGE #-}声明需要放在文件的最顶部，在module声明之前.

A {-# LANGUAGE #-} declaration needs to go at the very top of the file, before the module declaration.