Add mitems and mpairs where it makes sense

lib/pure/collections/lists.nim

@@ -122,6 +122,22 @@ iterator items*[T](L: DoublyLinkedRing[T]): T =
   ## yields every value of `L`.
   itemsRingImpl()
 
+iterator mitems*[T](L: var DoublyLinkedList[T]): var T =
+  ## yields every value of `L` so that you can modify it.
+  itemsListImpl()
+
+iterator mitems*[T](L: var SinglyLinkedList[T]): var T =
+  ## yields every value of `L` so that you can modify it.
+  itemsListImpl()
+
+iterator mitems*[T](L: var SinglyLinkedRing[T]): var T =
+  ## yields every value of `L` so that you can modify it.
+  itemsRingImpl()
+
+iterator mitems*[T](L: var DoublyLinkedRing[T]): var T =
+  ## yields every value of `L` so that you can modify it.
+  itemsRingImpl()
+
 iterator nodes*[T](L: SinglyLinkedList[T]): SinglyLinkedNode[T] = 
   ## iterates over every node of `x`. Removing the current node from the
   ## list during traversal is supported.

lib/pure/collections/queues.nim

@@ -39,6 +39,15 @@ iterator items*[T](q: Queue[T]): T =
     yield q.data[i]
     i = (i + 1) and q.mask
 
+iterator mitems*[T](q: var Queue[T]): var T =
+  ## yields every element of `q`.
+  var i = q.rd
+  var c = q.count
+  while c > 0:
+    dec c
+    yield q.data[i]
+    i = (i + 1) and q.mask
+
 proc add*[T](q: var Queue[T], item: T) =
   ## adds an `item` to the end of the queue `q`.
   var cap = q.mask+1