fix var/laziness bug in Foldable[List]

scalaz · Apr 3, 2012 · 48c29e13afbe165700ce860decf9aa50b0e5f52d · 48c29e1
1 parent 2b7faa1
commit 48c29e13afbe165700ce860decf9aa50b0e5f52d
Unified Split

Showing with 5 additions and 1 deletion.

+5 −1 core/src/main/scala/scalaz/std/List.scala
diff --git a/core/src/main/scala/scalaz/std/List.scala b/core/src/main/scala/scalaz/std/List.scala
@@ -64,7 +64,11 @@ trait ListInstances extends ListInstances0 {
       val s = new ArrayStack[A]
       fa.foreach(a => s += a)
       var r = z
-      while (!s.isEmpty) {r = f(s.pop, r)}
+      while (!s.isEmpty) {
+        // force and copy the value of r to ensure correctness
+        val w = r
+        r = f(s.pop, w)
+      }
       r
     }