Merge pull request #64 from hdgarrood/bug-63

Fix for issue #63

Author: garyb

src/Data/StrMap.js

@@ -47,17 +47,18 @@ exports._foldM = function (bind) {
   return function (f) {
     return function (mz) {
       return function (m) {
+        var acc = mz;
         function g(k) {
           return function (z) {
             return f(z)(k)(m[k]);
           };
         }
         for (var k in m) {
           if (m.hasOwnProperty(k)) {
-            mz = bind(mz)(g(k));
+            acc = bind(acc)(g(k));
           }
         }
-        return mz;
+        return acc;
       };
     };
   };

test/Test/Data/StrMap.purs

@@ -143,3 +143,12 @@ strMapTests = do
 
   log "fromFoldable = zip keys values"
   quickCheck $ \(TestStrMap m) -> M.toList m == zipWith Tuple (fromFoldable $ M.keys m) (M.values m :: List Int)
+
+  log "Bug #63: accidental observable mutation in foldMap"
+  quickCheck \(TestStrMap m) ->
+    let lhs = go m
+        rhs = go m
+    in lhs == rhs <?> ("lhs: " <> show lhs <> ", rhs: " <> show rhs)
+    where
+    go :: M.StrMap (Array Ordering) -> Array Ordering
+    go = M.foldMap \_ v -> v