Constrain base monad to MonadCatch

Let's try MonadThrow/MonadCatch. It looks nice at a first glance. The
monad transformer stack contains only the ReaderT, less lifts are
required. Exception subtyping is easier, the user can (and should)
define custom error types and throw them. And it is still possible to
use pure error handling, if someone doesn't like runtime exceptions or
need to run a query in a pure environment.

Fixes #42.

1 files changed, 17 insertions, 19 deletions

diff --git a/tests/Test/StarWars/Schema.hs b/tests/Test/StarWars/Schema.hs
index 99200ff..cecd8eb 100644
--- a/tests/Test/StarWars/Schema.hs
+++ b/tests/Test/StarWars/Schema.hs
@@ -4,10 +4,8 @@ module Test.StarWars.Schema
     ( schema
     ) where
 
+import Control.Monad.Catch (MonadThrow(..), SomeException)
 import Control.Monad.Trans.Reader (asks)
-import Control.Monad.Trans.Except (throwE)
-import Control.Monad.Trans.Class (lift)
-import Data.Functor.Identity (Identity)
 import qualified Data.HashMap.Strict as HashMap
 import Data.Maybe (catMaybes)
 import Data.Text (Text)
@@ -19,7 +17,7 @@ import Prelude hiding (id)
 
 -- See https://github.com/graphql/graphql-js/blob/master/src/__tests__/starWarsSchema.js
 
-schema :: Schema Identity
+schema :: Schema (Either SomeException)
 schema = Schema
     { query = queryType
     , mutation = Nothing
@@ -42,7 +40,7 @@ schema = Schema
     droidField = Out.Field Nothing (Out.NamedObjectType droidObject) mempty
     droidFieldResolver = ValueResolver droidField droid
 
-heroObject :: Out.ObjectType Identity
+heroObject :: Out.ObjectType (Either SomeException)
 heroObject = Out.ObjectType "Human" Nothing [] $ HashMap.fromList
     [ ("id", idFieldType)
     , ("name", nameFieldType)
@@ -57,7 +55,7 @@ heroObject = Out.ObjectType "Human" Nothing [] $ HashMap.fromList
       = ValueResolver (Out.Field Nothing (Out.NamedScalarType string) mempty)
       $ idField "homePlanet"
 
-droidObject :: Out.ObjectType Identity
+droidObject :: Out.ObjectType (Either SomeException)
 droidObject = Out.ObjectType "Droid" Nothing [] $ HashMap.fromList
     [ ("id", idFieldType)
     , ("name", nameFieldType)
@@ -72,29 +70,29 @@ droidObject = Out.ObjectType "Droid" Nothing [] $ HashMap.fromList
         = ValueResolver (Out.Field Nothing (Out.NamedScalarType string) mempty)
         $ idField "primaryFunction"
 
-typenameFieldType :: Resolver Identity
+typenameFieldType :: Resolver (Either SomeException)
 typenameFieldType
     = ValueResolver (Out.Field Nothing (Out.NamedScalarType string) mempty)
     $ idField "__typename"
 
-idFieldType :: Resolver Identity
+idFieldType :: Resolver (Either SomeException)
 idFieldType
     = ValueResolver (Out.Field Nothing (Out.NamedScalarType id) mempty)
     $ idField "id"
 
-nameFieldType :: Resolver  Identity
+nameFieldType :: Resolver (Either SomeException)
 nameFieldType
     = ValueResolver (Out.Field Nothing (Out.NamedScalarType string) mempty)
     $ idField "name"
 
-friendsFieldType :: Resolver Identity
+friendsFieldType :: Resolver (Either SomeException)
 friendsFieldType
     = ValueResolver (Out.Field Nothing fieldType mempty)
     $ idField "friends"
   where
     fieldType = Out.ListType $ Out.NamedObjectType droidObject
 
-appearsInField :: Resolver Identity
+appearsInField :: Resolver (Either SomeException)
 appearsInField
     = ValueResolver (Out.Field (Just description) fieldType mempty)
     $ idField "appearsIn"
@@ -102,14 +100,14 @@ appearsInField
     fieldType = Out.ListType $ Out.NamedEnumType episodeEnum
     description = "Which movies they appear in."
 
-secretBackstoryFieldType :: Resolver Identity
+secretBackstoryFieldType :: Resolver (Either SomeException)
 secretBackstoryFieldType = ValueResolver field secretBackstory
   where
     field = Out.Field Nothing (Out.NamedScalarType string) mempty
 
-idField :: Text -> Resolve Identity
+idField :: Text -> Resolve (Either SomeException)
 idField f = do
-    v <- lift $ asks values
+    v <- asks values
     let (Object v') = v
     pure $ v' HashMap.! f
 
@@ -122,7 +120,7 @@ episodeEnum = EnumType "Episode" (Just description)
     empire = ("EMPIRE", EnumValue $ Just "Released in 1980.")
     jedi = ("JEDI", EnumValue $ Just "Released in 1983.")
 
-hero :: Resolve Identity
+hero :: Resolve (Either SomeException)
 hero = do
   episode <- argument "episode"
   pure $ character $ case episode of
@@ -131,19 +129,19 @@ hero = do
       Enum "JEDI" -> getHero 6
       _ -> artoo
 
-human :: Resolve Identity
+human :: Resolve (Either SomeException)
 human = do
     id' <- argument "id"
     case id' of
         String i -> pure $ maybe Null character $ getHuman i >>= Just
-        _ -> throwE "Invalid arguments."
+        _ -> throwM InvalidArguments
 
-droid :: Resolve Identity
+droid :: Resolve (Either SomeException)
 droid = do
     id' <- argument "id"
     case id' of
         String i -> pure $ maybe Null character $ getDroid i >>= Just
-        _ -> throwE "Invalid arguments."
+        _ -> throwM InvalidArguments
 
 character :: Character -> Value
 character char = Object $ HashMap.fromList