[英]Getting the data constructor name as a string using GHC.Generics
我喜欢以下内容:
constrName :: Data a=> a -> String
constrName = showConstr . toConstr
但是对于GHC.Generics
。 我看到了Constructor
类,但没有看到范围内的任何实例。 我正在使用base-4.8.1.0
。
Nathan Howell改编这个要点: 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
我们可以做的:
*Main> constrName (Bar 1)
"Bar"
*Main> constrName $ X 'a'
"X"
*Main> constrName Y
"Y"
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