graphql/src/Language/GraphQL/Error.hs

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{-# LANGUAGE OverloadedStrings #-}
module Language.GraphQL.Error
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( parseError
, CollectErrsT
, addErr
, addErrMsg
, runCollectErrs
, runAppendErrs
) where
import qualified Data.Aeson as Aeson
import Data.Text (Text, pack)
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import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.State ( StateT
, modify
, runStateT
)
-- | Wraps a parse error into a list of errors.
parseError :: Applicative f => String -> f Aeson.Value
parseError s =
pure $ Aeson.object [("errors", Aeson.toJSON [makeErrorMsg $ pack s])]
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-- | A wrapper to pass error messages around.
type CollectErrsT m = StateT [Aeson.Value] m
-- | Adds an error to the list of errors.
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addErr :: Monad m => Aeson.Value -> CollectErrsT m ()
addErr v = modify (v :)
makeErrorMsg :: Text -> Aeson.Value
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makeErrorMsg s = Aeson.object [("message", Aeson.toJSON s)]
-- | Convenience function for just wrapping an error message.
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addErrMsg :: Monad m => Text -> CollectErrsT m ()
addErrMsg = addErr . makeErrorMsg
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-- | Appends the given list of errors to the current list of errors.
appendErrs :: Monad m => [Aeson.Value] -> CollectErrsT m ()
appendErrs errs = modify (errs ++)
-- | Runs the given query computation, but collects the errors into an error
-- list, which is then sent back with the data.
runCollectErrs :: Monad m => CollectErrsT m Aeson.Value -> m Aeson.Value
runCollectErrs res = do
(dat, errs) <- runStateT res []
if null errs
then return $ Aeson.object [("data", dat)]
else return $ Aeson.object [("data", dat), ("errors", Aeson.toJSON $ reverse errs)]
-- | Runs the given computation, collecting the errors and appending them
-- to the previous list of errors.
runAppendErrs :: Monad m => CollectErrsT m a -> CollectErrsT m a
runAppendErrs f = do
(v, errs) <- lift $ runStateT f []
appendErrs errs
return v