Generic read for enum types (based on lowercase constructor names) using generics-sop

EnumRead.hs

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE MonoLocalBinds #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
module EnumRead where

import Data.Char
import qualified Data.Map
import Generics.SOP
import Generics.SOP.NS

enumRead :: forall a . (IsEnumType a, HasDatatypeInfo a) => String -> Maybe a
enumRead = flip Data.Map.lookup table
  where
    table =
      Data.Map.fromList
        (hcollapse
          (hzipWith
            (\ c (K r) -> K (map toLower (constructorName c), to (SOP r)))
            (constructorInfo (datatypeInfo (Proxy @a))) -- metadata for all constructors
            (apInjs'_NP (hcpure (Proxy @((~) '[])) Nil)) -- representation of all values
          )
        )