pretty-printing of config value sources

1 files changed, 12 insertions, 2 deletions

diff --git a/src/Conftrack/Value.hs b/src/Conftrack/Value.hs
index fef8f87..50e4e30 100644
--- a/src/Conftrack/Value.hs
+++ b/src/Conftrack/Value.hs
@@ -6,6 +6,7 @@
 {-# LANGUAGE StrictData #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE DefaultSignatures #-}
 
 module Conftrack.Value (key, Value(..), ConfigError(..), Key(..), ConfigValue(..), Origin(..), KeyPart, prefixedWith) where
 
@@ -58,9 +59,15 @@ data ConfigError =
 
 class ConfigValue a where
   fromConfig :: Value -> Either ConfigError a
+  prettyValue :: a -> Text
 
-data Origin = Origin Key Text
-  deriving Show
+  default prettyValue :: Show a => a -> Text
+  prettyValue = T.pack . show
+
+data Origin = forall a. ConfigValue a => Origin a Text
+
+instance Show Origin where
+  show (Origin a text) = "Origin " <> T.unpack (prettyValue a) <> " " <> T.unpack text
 
 withString :: (BS.ByteString -> Either ConfigError a) -> Value -> Either ConfigError a
 withString f (ConfigString a) = f a
@@ -89,6 +96,9 @@ instance ConfigValue a => ConfigValue (Maybe a) where
   fromConfig ConfigNull = Right Nothing
   fromConfig just = fmap Just (fromConfig just)
 
+  prettyValue Nothing = "null"
+  prettyValue (Just a) = prettyValue a
+
 instance ConfigValue OsPath where
   fromConfig = \case
     (ConfigString text) -> stringToPath text