git.iko.soy/rel8
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Have ReadShow describe what it's trying to read
444bf05Ollie Charles
src/Rel8/Type/ReadShow.hs+11−3
compare with master
unifiedsplit
@@ -1,8 +1,14 @@
1+{-# language ScopedTypeVariables #-}
2+{-# language TypeApplications #-}
3+{-# language ViewPatterns #-}
4+
1module Rel8.Type.ReadShow ( ReadShow(..) ) where
5module Rel8.Type.ReadShow ( ReadShow(..) ) where
2
6
3-- base
7-- base
8+import Data.Proxy ( Proxy( Proxy ) )
9+import Data.Typeable ( Typeable, typeRep )
4import Prelude
10import Prelude
5−import Text.Read ( readEither )
11+import Text.Read ( readMaybe )
6
12
7-- rel8
13-- rel8
8import Rel8.Type ( DBType( typeInformation ) )
14import Rel8.Type ( DBType( typeInformation ) )
@@ -17,8 +23,10 @@ import qualified Data.Text as Text
17newtype ReadShow a = ReadShow { fromReadShow :: a }
23newtype ReadShow a = ReadShow { fromReadShow :: a }
18
24
19
25
20−instance (Read a, Show a) => DBType (ReadShow a) where
26+instance (Read a, Show a, Typeable a) => DBType (ReadShow a) where
21 typeInformation = parseTypeInformation parser printer typeInformation
27 typeInformation = parseTypeInformation parser printer typeInformation
22 where
28 where
23− parser = fmap ReadShow . readEither . Text.unpack
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))
24 printer = Text.pack . show . fromReadShow
32 printer = Text.pack . show . fromReadShow