[#12] implement forEach to iterate of query snapshot

Author: marcosh

src/Web/Firestore/QuerySnapshot.js

@@ -0,0 +1,9 @@
+"use strict";
+
+exports.forEachImpl = function (snapshot, callback) {
+  return function () {
+    return snapshot.forEach(function (documentSnapshot) {
+      return callback(documentSnapshot)()
+    })
+  }
+}

src/Web/Firestore/QuerySnapshot.purs

@@ -1,3 +1,14 @@
 module Web.Firestore.QuerySnapshot where
 
+import Prelude
+import Data.Function.Uncurried (Fn2, runFn2)
+import Effect (Effect)
+
 foreign import data QuerySnapshot :: Type -> Type
+
+foreign import data QueryDocumentSnapshot :: Type -> Type
+
+foreign import forEachImpl :: forall a. Fn2 (QuerySnapshot a) (QueryDocumentSnapshot a -> Effect Unit) (Effect Unit)
+
+forEach :: forall a. QuerySnapshot a -> (QueryDocumentSnapshot a -> Effect Unit) -> Effect Unit
+forEach = runFn2 forEachImpl