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Created March 19, 2018 10:49
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Generic read for enum types (based on lowercase constructor names) using generics-sop
{-# 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
table =
(\ 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
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