使用GHC.Generics获取数据构造函数名称作为字符串 [英] Getting the data constructor name as a string using GHC.Generics
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问题描述
我想要以下内容:
constrName :: Data a=> a -> String
constrName = showConstr . toConstr
但对于GHC.Generics
.我看到了Constructor
类,但是没有看到范围内的任何实例.我正在使用base-4.8.1.0
.
But for GHC.Generics
. I see the Constructor
class, but don't see any instances in scope. I'm using base-4.8.1.0
.
推荐答案
Nathan Howell修改的要点: https ://gist.github.com/NathanHowell/6201625 :
Adapting this gist by Nathan Howell: https://gist.github.com/NathanHowell/6201625 :
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE TypeSynonymInstances #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE FlexibleContexts #-}
import GHC.Generics
constrName :: (HasConstructor (Rep a), Generic a)=> a -> String
constrName = genericConstrName . from
class HasConstructor (f :: * -> *) where
genericConstrName :: f x -> String
instance HasConstructor f => HasConstructor (D1 c f) where
genericConstrName (M1 x) = genericConstrName x
instance (HasConstructor x, HasConstructor y) => HasConstructor (x :+: y) where
genericConstrName (L1 l) = genericConstrName l
genericConstrName (R1 r) = genericConstrName r
instance Constructor c => HasConstructor (C1 c f) where
genericConstrName x = conName x
--------------
data Foo = Bar Int | Baz Float deriving Generic
newtype X = X Char deriving Generic
data Y = Y deriving Generic
我们可以做到:
*Main> constrName (Bar 1)
"Bar"
*Main> constrName $ X 'a'
"X"
*Main> constrName Y
"Y"
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