相关疑难解决方法(0)

This code is compiled fine:

data None = None { _f :: Int }
type Simpl = Env

type Env = Int

However, I got an error with this code:

{-# LANGUAGE TemplateHaskell #-}
import Control.Lens

data None = None { _f :: Int }

type Simpl = Env

makeLenses ''None

type Env = Int

Error:

Not in scope: type constructor or class `Env'

I just added a single line makeLenses ''None between type declarations.
This means TemplateHaskell code could …