3 files changed, 13 insertions, 11 deletions
diff --git a/src/Language/GraphQL/AST/Document.hs b/src/Language/GraphQL/AST/Document.hs
index ed473b7..cd1dbc6 100644
--- a/src/Language/GraphQL/AST/Document.hs
+++ b/src/Language/GraphQL/AST/Document.hs
@@ -99,9 +99,7 @@ data OperationDefinition
 -- * mutation - a write operation followed by a fetch.
 -- * subscription - a long-lived request that fetches data in response to
 -- source events.
---
--- Currently only queries and mutations are supported.
-data OperationType = Query | Mutation deriving (Eq, Show)
+data OperationType = Query | Mutation | Subscription deriving (Eq, Show)
 
 -- ** Selection Sets
 
diff --git a/src/Language/GraphQL/AST/Encoder.hs b/src/Language/GraphQL/AST/Encoder.hs
index a9f91ec..b55566d 100644
--- a/src/Language/GraphQL/AST/Encoder.hs
+++ b/src/Language/GraphQL/AST/Encoder.hs
@@ -1,5 +1,6 @@
-{-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE LambdaCase #-}
 
 -- | This module defines a minifier and a printer for the @GraphQL@ language.
 module Language.GraphQL.AST.Encoder
@@ -65,12 +66,14 @@ definition formatter x
 
 -- | Converts a 'OperationDefinition into a string.
 operationDefinition :: Formatter -> OperationDefinition -> Lazy.Text
-operationDefinition formatter (SelectionSet sels)
-    = selectionSet formatter sels
-operationDefinition formatter (OperationDefinition Query name vars dirs sels)
-    = "query " <> node formatter name vars dirs sels
-operationDefinition formatter (OperationDefinition Mutation name vars dirs sels)
-    = "mutation " <> node formatter name vars dirs sels
+operationDefinition formatter = \case
+    SelectionSet sels -> selectionSet formatter sels
+    OperationDefinition Query name vars dirs sels ->
+        "query " <> node formatter name vars dirs sels
+    OperationDefinition Mutation name vars dirs sels ->
+        "mutation " <> node formatter name vars dirs sels
+    OperationDefinition Subscription name vars dirs sels ->
+        "subscription " <> node formatter name vars dirs sels
 
 -- | Converts a Query or Mutation into a string.
 node :: Formatter ->
diff --git a/src/Language/GraphQL/AST/Parser.hs b/src/Language/GraphQL/AST/Parser.hs
index 150586e..ea517da 100644
--- a/src/Language/GraphQL/AST/Parser.hs
+++ b/src/Language/GraphQL/AST/Parser.hs
@@ -334,7 +334,8 @@ operationDefinition = SelectionSet <$> selectionSet
 operationType :: Parser OperationType
 operationType = Query <$ symbol "query"
     <|> Mutation <$ symbol "mutation"
-    -- <?> Keep default error message
+    <|> Subscription <$ symbol "subscription"
+    <?> "OperationType"
 
 selectionSet :: Parser SelectionSet
 selectionSet = braces (NonEmpty.some selection) <?> "SelectionSet"