Fix iterating over an empty list.

builtin/core.wren

@@ -10,17 +10,13 @@ class List {
   }
 
   + that {
-    var newList = []
-    if (this.count > 0) {
-      for (element in this) {
-        newList.add(element)
-      }
+    var result = []
+    for (element in this) {
+      result.add(element)
     }
-    if (that is Range || that.count > 0) {
-      for (element in that) {
-        newList.add(element)
-      }
+    for (element in that) {
+      result.add(element)
     }
-    return newList
+    return result
   }
 }

src/wren_core.c

@@ -53,18 +53,14 @@ static const char* libSource =
 "  }\n"
 "\n"
 "  + that {\n"
-"    var newList = []\n"
-"    if (this.count > 0) {\n"
-"      for (element in this) {\n"
-"        newList.add(element)\n"
-"      }\n"
+"    var result = []\n"
+"    for (element in this) {\n"
+"      result.add(element)\n"
 "    }\n"
-"    if (that is Range || that.count > 0) {\n"
-"      for (element in that) {\n"
-"        newList.add(element)\n"
-"      }\n"
+"    for (element in that) {\n"
+"      result.add(element)\n"
 "    }\n"
-"    return newList\n"
+"    return result\n"
 "  }\n"
 "}\n";
 
@@ -336,12 +332,17 @@ DEF_NATIVE(list_insert)
 
 DEF_NATIVE(list_iterate)
 {
+  ObjList* list = AS_LIST(args[0]);
+
   // If we're starting the iteration, return the first index.
-  if (IS_NULL(args[1])) RETURN_NUM(0);
+  if (IS_NULL(args[1]))
+  {
+    if (list->count == 0) RETURN_FALSE;
+    RETURN_NUM(0);
+  }
 
   if (!validateInt(vm, args, 1, "Iterator")) return PRIM_ERROR;
 
-  ObjList* list = AS_LIST(args[0]);
   int index = (int)AS_NUM(args[1]);
 
   // Stop if we're out of bounds.

test/list/iterate.wren

@@ -5,3 +5,6 @@ IO.print(a.iterate(1)) // expect: 2
 IO.print(a.iterate(2)) // expect: 3
 IO.print(a.iterate(3)) // expect: false
 IO.print(a.iterate(-1)) // expect: false
+
+// Nothing to iterate in an empty list.
+IO.print([].iterate(null)) // expect: false

test/list/plus.wren

@@ -13,3 +13,6 @@ IO.print(d) // expect: [1, 2, 3, 4, 5, 6]
 IO.print(e) // expect: [1, 2, 3]
 IO.print(f) // expect: [1, 2, 3]
 IO.print(g) // expect: []
+
+// Doesn't modify original list.
+IO.print(a) // expect: [1, 2, 3]