src/Rel8/Type/ReadShow.hs · rel8

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rel8/src/Rel8/Type/ReadShow.hs

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1module Rel8.Type.ReadShow ( ReadShow(..) ) where

3-- base

4import Prelude

5import Text.Read ( readEither )

7-- rel8

8import Rel8.Type ( DBType( typeInformation ) )

9import Rel8.Type.Information ( parseTypeInformation )

11-- text

12import qualified Data.Text as Text

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

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

18-- The declaration:

19--

20-- >>> :{

21-- data Color = Red | Green | Blue

22-- deriving (Read, Show)

23-- deriving PrimitiveType via ReadShow Color

24-- :}

25--

26-- will allow you to store @Color@ values in a single SQL column (stored as

27-- @text@).

28newtype ReadShow a = ReadShow { fromReadShow :: a }

31-- | The 'PrimitiveType' instance for 'ReadShow' allows you to serialize a type using

32-- Haskell's 'Read' and 'Show' instances:

34-- @

35-- data Color = Red | Green | Blue

36-- deriving (Read, Show)

37-- deriving PrimitiveType via ReadShow Color

38-- @

39instance (Read a, Show a) => DBType (ReadShow a) where

40 typeInformation = parseTypeInformation parser printer typeInformation

41 where

42 parser = fmap ReadShow . readEither . Text.unpack

43 printer = Text.pack . show . fromReadShow