Replace substitution function with a map

It makes using variables with queries more approachable, but some work
still has to be done.
- The type `Subs` should be renamed and moved out of `Schema`, together with
`AST.Core.Value` probably.
- Some kind of conversion should be possible from a user-defined input
type T to the Value. So the final HashMap should have a type like
`HashMap name a`, where a is an instance of a potential typeclass
InputType.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/Language/GraphQL/Schema.hs b/src/Language/GraphQL/Schema.hs
index fa8bf78..facf722 100644
--- a/src/Language/GraphQL/Schema.hs
+++ b/src/Language/GraphQL/Schema.hs
@@ -44,8 +44,9 @@ data Resolver m = Resolver
     Text -- ^ Name
     (Field -> CollectErrsT m Aeson.Object) -- ^ Resolver
 
--- | Variable substitution function.
-type Subs = Name -> Maybe Value
+-- | Contains variables for the query. The key of the map is a variable name,
+--   and the value is the variable value.
+type Subs = HashMap Name Value
 
 -- | Create a new 'Resolver' with the given 'Name' from the given 'Resolver's.
 object :: MonadIO m => Name -> ActionT m [Resolver m] -> Resolver m