Split AST in 2

One AST is meant to be a target parser and tries to adhere as much as possible
to the spec. The other is a simplified version of that AST meant for execution.

Also newtypes have been replaced by type synonyms and NonEmpty lists are being
used where it makes sense.

Data/GraphQL/Schema.hs

@@ -3,7 +3,7 @@
 -- | This module provides a representation of a @GraphQL@ Schema in addition to
 --   functions for defining and manipulating Schemas.
 module Data.GraphQL.Schema
-  ( Schema(..)
+  ( Schema
   , Resolver
   , Subs
   , object
@@ -15,31 +15,31 @@ module Data.GraphQL.Schema
   , enum
   , enumA
   , resolvers
-  , fields
   -- * AST Reexports
   , Field
   , Argument(..)
   , Value(..)
   ) where
 
-import Data.Bifunctor (first)
-import Data.Monoid (Alt(Alt,getAlt))
 import Control.Applicative (Alternative((<|>), empty))
-import Data.Maybe (catMaybes)
+import Data.Bifunctor (first)
 import Data.Foldable (fold)
+import Data.List.NonEmpty (NonEmpty)
+import Data.Maybe (fromMaybe)
+import Data.Monoid (Alt(Alt,getAlt))
 
 import qualified Data.Aeson as Aeson
 import Data.HashMap.Strict (HashMap)
 import qualified Data.HashMap.Strict as HashMap
 import Data.Text (Text)
-import qualified Data.Text as T (null, unwords)
+import qualified Data.Text as T (unwords)
 
-import Data.GraphQL.AST
+import Data.GraphQL.AST.Core
 import Data.GraphQL.Error
 
 -- | A GraphQL schema.
 --   @f@ is usually expected to be an instance of 'Alternative'.
-data Schema f = Schema [Resolver f]
+type Schema f = NonEmpty (Resolver f)
 
 -- | Resolves a 'Field' into an @Aeson.@'Aeson.Object' with error information
 --   (or 'empty'). @f@ is usually expected to be an instance of 'Alternative'.
@@ -48,18 +48,16 @@ type Resolver f = Field -> CollectErrsT f Aeson.Object
 -- | Variable substitution function.
 type Subs = Text -> Maybe Text
 
--- | Create a named 'Resolver' from a list of 'Resolver's.
-object :: Alternative f => Text -> [Resolver f] -> Resolver f
+object :: Alternative f => Name -> [Resolver f] -> Resolver f
 object name resolvs = objectA name $ \case
-     [] -> resolvs
-     _  -> empty
+      [] -> resolvs
+      _  -> empty
 
 -- | Like 'object' but also taking 'Argument's.
 objectA
   :: Alternative f
-  => Text -> ([Argument] -> [Resolver f]) -> Resolver f
-objectA name f fld@(Field _ _ args _ sels) =
-    withField name (resolvers (f args) $ fields sels) fld
+  => Name -> ([Argument] -> [Resolver f]) -> Resolver f
+objectA name f fld@(Field _ _ args sels) = withField name (resolvers (f args) sels) fld
 
 -- | A scalar represents a primitive value, like a string or an integer.
 scalar :: (Alternative f, Aeson.ToJSON a) => Text -> a -> Resolver f
@@ -70,11 +68,10 @@ scalar name s = scalarA name $ \case
 -- | Like 'scalar' but also taking 'Argument's.
 scalarA
   :: (Alternative f, Aeson.ToJSON a)
-  => Text -> ([Argument] -> f a) -> Resolver f
-scalarA name f fld@(Field _ _ args _ []) = withField name (errWrap $ f args) fld
+  => Name -> ([Argument] -> f a) -> Resolver f
+scalarA name f fld@(Field _ _ args []) = withField name (errWrap $ f args) fld
 scalarA _ _ _ = empty
 
--- | Like 'object' but taking lists of 'Resolver's instead of a single list.
 array :: Alternative f => Text -> [[Resolver f]] -> Resolver f
 array name resolvs = arrayA name $ \case
     [] -> resolvs
@@ -84,8 +81,8 @@ array name resolvs = arrayA name $ \case
 arrayA
   :: Alternative f
   => Text -> ([Argument] -> [[Resolver f]]) -> Resolver f
-arrayA name f fld@(Field _ _ args _ sels) =
-     withField name (joinErrs $ traverse (flip resolvers $ fields sels) $ f args) fld
+arrayA name f fld@(Field _ _ args sels) =
+     withField name (joinErrs $ traverse (`resolvers` sels) $ f args) fld
 
 -- | Represents one of a finite set of possible values.
 --   Used in place of a 'scalar' when the possible responses are easily enumerable.
@@ -96,19 +93,19 @@ enum name enums = enumA name $ \case
 
 -- | Like 'enum' but also taking 'Argument's.
 enumA :: Alternative f => Text -> ([Argument] -> f [Text]) -> Resolver f
-enumA name f fld@(Field _ _ args _ []) = withField name (errWrap $ f args) fld
+enumA name f fld@(Field _ _ args []) = withField name (errWrap $ f args) fld
 enumA _ _ _ = empty
 
 -- | Helper function to facilitate 'Argument' handling.
 withField
   :: (Alternative f, Aeson.ToJSON a)
-  => Text -> CollectErrsT f a -> Field -> CollectErrsT f (HashMap Text Aeson.Value)
-withField name f (Field alias name' _ _ _) =
+  => Name -> CollectErrsT f a -> Field -> CollectErrsT f (HashMap Text Aeson.Value)
+withField name f (Field alias name' _ _) =
      if name == name'
         then fmap (first $ HashMap.singleton aliasOrName . Aeson.toJSON) f
         else empty
      where
-       aliasOrName = if T.null alias then name' else alias
+       aliasOrName = fromMaybe name' alias
 
 -- | Takes a list of 'Resolver's and a list of 'Field's and applies each
 --   'Resolver' to each 'Field'. Resolves into a value containing the
@@ -118,18 +115,8 @@ resolvers resolvs =
     fmap (first Aeson.toJSON . fold)
   . traverse (\fld -> getAlt (foldMap (Alt . ($ fld)) resolvs) <|> errmsg fld)
   where
-    errmsg (Field alias name _ _ _) = addErrMsg msg $ (errWrap . pure) val
+    errmsg (Field alias name _ _) = addErrMsg msg $ (errWrap . pure) val
        where
          val = HashMap.singleton aliasOrName Aeson.Null
          msg = T.unwords ["field", name, "not resolved."]
-         aliasOrName = if T.null alias then name else alias
-
--- | Checks whether the given 'Selection' contains a 'Field' and
---   returns the 'Field' if so, else returns 'Nothing'.
-field :: Selection -> Maybe Field
-field (SelectionField x) = Just x
-field _ = Nothing
-
--- | Returns a list of the 'Field's contained in the given 'SelectionSet'.
-fields :: SelectionSet -> [Field]
-fields = catMaybes . fmap field
+         aliasOrName = fromMaybe name alias