Overhaul Schema DSL

Aside of making the definition of Schemas easier, it takes care of
issues like nested aliases which previously wasn't possible. The naming
of the DSL functions is still provisional.

Data/GraphQL/Execute.hs

@@ -2,64 +2,41 @@
 module Data.GraphQL.Execute (execute) where
 
 #if !MIN_VERSION_base(4,8,0)
-import Control.Applicative ((<$>), pure)
-import Data.Traversable (traverse)
+import Control.Applicative ((<$>))
 #endif
-import Control.Applicative (Alternative, empty)
-import Data.Foldable (fold)
+import Control.Applicative (Alternative)
 import Data.Maybe (catMaybes)
 
 import qualified Data.Aeson as Aeson
-import qualified Data.HashMap.Strict as HashMap
-import qualified Data.Text as T
 
 import Data.GraphQL.AST
-import Data.GraphQL.Schema (Resolver, Schema(..))
+import Data.GraphQL.Schema (Schema(..))
 import qualified Data.GraphQL.Schema as Schema
 
 execute
-  :: (Alternative m, Monad m)
+  :: Alternative m
   => Schema m -> Schema.Subs -> Document -> m Aeson.Value
-execute (Schema resolv) f doc = selectionSet f resolv =<< query doc
+execute (Schema resolvm) subs =
+   fmap Aeson.toJSON . Schema.withFields resolvm . rootFields subs
 
-query :: Alternative f => Document -> f SelectionSet
-query (Document [DefinitionOperation (Query (Node _varDefs _ _ sels))]) = pure sels
-query  _ = empty
+rootFields :: Schema.Subs -> Document -> [Field]
+rootFields subs (Document [DefinitionOperation (Query (Node _varDefs _ _ sels))]) =
+    Schema.fields $ substitute subs <$> sels
+rootFields _ _ = []
 
-selectionSet
-  :: Alternative f
-  => Schema.Subs -> Resolver f -> SelectionSet -> f Aeson.Value
-selectionSet f resolv = fmap (Aeson.Object . fold)
-                      . traverse (selection f resolv)
+substitute :: Schema.Subs -> Selection -> Selection
+substitute subs (SelectionField (Field alias name args directives sels)) =
+    SelectionField $ Field
+      alias
+      name
+      -- TODO: Get rid of `catMaybes`, invalid arguments should raise an error
+      (catMaybes $ subsArg subs <$> args)
+      directives
+      (substitute subs <$> sels)
+substitute _ sel = sel
 
-selection
-  :: Alternative f
-  => Schema.Subs -> Resolver f -> Selection -> f Aeson.Object
-selection f resolv (SelectionField field@(Field alias name _ _ _)) =
-    fmap (HashMap.singleton aliasOrName)
-      $  Aeson.toJSON
-     <$> resolv (fieldToInput f field)
-  where
-    aliasOrName = if T.null alias then name else alias
-selection _ _ _ = empty
-
--- * AST/Schema conversions
-
-argument :: Schema.Subs -> Argument -> Maybe Schema.Argument
-argument f (Argument n (ValueVariable (Variable v))) =
-    maybe Nothing (\v' -> Just (n, v')) $ f v
-argument _ (Argument n (ValueInt v)) =
-    Just (n, Schema.ScalarInt $ fromIntegral v)
-argument _ (Argument n (ValueString (StringValue v))) =
-    Just (n, Schema.ScalarString v)
-argument _ _ = error "argument: not implemented yet"
-
-fieldToInput :: Schema.Subs -> Field -> Schema.Input
-fieldToInput f (Field _ n as _ sels) =
-    -- TODO: Get rid of `catMaybes`, invalid arguments should raise an error
-    Schema.InputField n (catMaybes $ argument f <$> as)
-                        (fieldToInput f . selectionToField <$> sels)
-
-selectionToField :: Selection -> Field
-selectionToField (SelectionField x) = x
-selectionToField _ = error "selectionField: not implemented yet"
+-- TODO: Support different value types
+subsArg :: Schema.Subs -> Argument -> Maybe Argument
+subsArg subs (Argument n (ValueVariable (Variable v))) =
+    Argument n . ValueString . StringValue <$> subs v
+subsArg _ arg = Just arg

Data/GraphQL/Schema.hs

@@ -1,20 +1,46 @@
 {-# LANGUAGE CPP #-}
-module Data.GraphQL.Schema where
+module Data.GraphQL.Schema
+  ( Schema(..)
+  , QueryRoot
+  , ResolverO
+  , ResolverM
+  , Output(..)
+  , Subs
+  , Scalar(..)
+  , withField
+  , withFieldFinal
+  , withFields
+  , withArgument
+  , outputTraverse
+  , fields
+  -- * Reexports
+  , Field
+  , Argument
+  ) where
 
 #if !MIN_VERSION_base(4,8,0)
-import Control.Applicative ((<$>))
+import Data.Traversable (traverse)
 #endif
+import Control.Applicative
+import Data.Maybe (catMaybes)
+import Data.Foldable (fold)
 import Data.String (IsString(fromString))
 
 import Data.Aeson (ToJSON(toJSON))
 import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
 import Data.Text (Text, pack)
+import qualified Data.Text as T (null)
+
+import Data.GraphQL.AST
 
 data Schema f = Schema (QueryRoot f)
 
-type QueryRoot f = Resolver f
+type QueryRoot f = ResolverM f
 
-type Resolver f = Input -> f Output
+-- TODO: Come up with a unique data type or better renaming
+type ResolverM f =  Field  -> f (HashMap Text Output)
+type ResolverO f = [Field] -> f Output
 
 data Output = OutputObject (HashMap Text Output)
             | OutputList [Output]
@@ -22,12 +48,7 @@ data Output = OutputObject (HashMap Text Output)
             | OutputEnum Text
               deriving (Show)
 
-type Argument = (Text, Scalar)
-
-type Subs = Text -> Maybe Scalar
-
-data Input = InputField Text [Argument] [Input]
-             deriving (Show)
+type Subs = Text -> Maybe Text
 
 -- TODO: GraphQL spec for Integer Scalar is 32bits
 data Scalar = ScalarInt     Int
@@ -53,3 +74,38 @@ instance ToJSON Output where
     toJSON (OutputScalar x) = toJSON x
     toJSON (OutputEnum   x) = toJSON x
 
+-- * Helpers
+
+withField :: Alternative f => Text -> ([Argument] -> ResolverO f) -> ResolverM f
+withField n f (Field alias name' args _ sels) =
+  if n == name'
+     then HashMap.singleton aliasOrName <$> f args (fields sels)
+     else empty
+  where
+    aliasOrName = if T.null alias then name' else alias
+
+withFieldFinal :: Alternative f => Text -> Output -> ResolverM f
+withFieldFinal n o fld@(Field _ _ [] _ []) = withField n (\_ _ -> pure o) fld
+withFieldFinal _ _ _ = empty
+
+withFields :: Alternative f => ResolverM f -> ResolverO f
+withFields f = fmap (OutputObject . fold) . traverse f
+
+outputTraverse :: Applicative f => (a -> f Output) -> [a] -> f Output
+outputTraverse f = fmap OutputList . traverse f
+
+withArgument :: Text -> [Argument] -> Maybe Scalar
+withArgument x [Argument n s] = if x == n then scalarValue s else Nothing
+withArgument _ _ = Nothing
+
+scalarValue :: Value -> Maybe Scalar
+scalarValue (ValueInt x) = Just . ScalarInt $ fromIntegral x
+scalarValue (ValueString (StringValue x)) = Just $ ScalarString x
+scalarValue _ = Nothing
+
+fields :: SelectionSet -> [Field]
+fields = catMaybes . fmap field
+
+field :: Selection -> Maybe Field
+field (SelectionField x) = Just x
+field _ = Nothing