src/Rel8/Type/ReadShow.hs · rel8

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rel8/src/Rel8/Type/ReadShow.hs

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1{-# language ScopedTypeVariables #-}

2{-# language TypeApplications #-}

3{-# language ViewPatterns #-}

5module Rel8.Type.ReadShow ( ReadShow(..) ) where

7-- base

8import Data.Proxy ( Proxy( Proxy ) )

9import Data.Typeable ( Typeable, typeRep )

10import Prelude

11import Text.Read ( readMaybe )

13-- rel8

14import Rel8.Type ( DBType( typeInformation ) )

15import Rel8.Type.Information ( parseTypeInformation )

17-- text

18import qualified Data.Text as Text

21-- | A deriving-via helper type for column types that store a Haskell value

22-- using a Haskell's 'Read' and 'Show' type classes.

23newtype ReadShow a = ReadShow { fromReadShow :: a }

26instance (Read a, Show a, Typeable a) => DBType (ReadShow a) where

27 typeInformation = parseTypeInformation parser printer typeInformation

28 where

29 parser (Text.unpack -> t) = case readMaybe t of

30 Just ok -> Right $ ReadShow ok

31 Nothing -> Left $ "Could not read " <> t <> " as a " <> show (typeRep (Proxy @a))

32 printer = Text.pack . show . fromReadShow