3 files changed, 53 insertions, 43 deletions

diff --git a/src/pkg/container/list/Makefile b/src/pkg/container/list/Makefile
index 2d5b35715..7fcd5f99a 100644
--- a/src/pkg/container/list/Makefile
+++ b/src/pkg/container/list/Makefile
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
-include ../../../Make.$(GOARCH)
+include ../../../Make.inc
 
 TARG=container/list
 GOFILES=\
diff --git a/src/pkg/container/list/list.go b/src/pkg/container/list/list.go
index 40c968099..c1ebcddaa 100644
--- a/src/pkg/container/list/list.go
+++ b/src/pkg/container/list/list.go
@@ -3,6 +3,12 @@
 // license that can be found in the LICENSE file.
 
 // The list package implements a doubly linked list.
+//
+// To iterate over a list (where l is a *List):
+//	for e := l.Front(); e != nil; e = e.Next() {
+//		// do something with e.Value
+//	}
+//
 package list
 
 // Element is an element in the linked list.
@@ -11,8 +17,8 @@ type Element struct {
 	// The front of the list has prev = nil, and the back has next = nil.
 	next, prev *Element
 
-	// A unique ID for the list to which this element belongs.
-	id *byte
+	// The list to which this element belongs.
+	list *List
 
 	// The contents of this list element.
 	Value interface{}
@@ -25,10 +31,10 @@ func (e *Element) Next() *Element { return e.next }
 func (e *Element) Prev() *Element { return e.prev }
 
 // List represents a doubly linked list.
+// The zero value for List is an empty list ready to use.
 type List struct {
 	front, back *Element
 	len         int
-	id          *byte
 }
 
 // Init initializes or clears a List.
@@ -36,12 +42,11 @@ func (l *List) Init() *List {
 	l.front = nil
 	l.back = nil
 	l.len = 0
-	l.id = new(byte)
 	return l
 }
 
 // New returns an initialized list.
-func New() *List { return new(List).Init() }
+func New() *List { return new(List) }
 
 // Front returns the first element in the list.
 func (l *List) Front() *Element { return l.front }
@@ -49,9 +54,19 @@ func (l *List) Front() *Element { return l.front }
 // Back returns the last element in the list.
 func (l *List) Back() *Element { return l.back }
 
-// Remove removes the element from the list.
-func (l *List) Remove(e *Element) {
-	if e.id != l.id {
+// Remove removes the element from the list
+// and returns its Value.
+func (l *List) Remove(e *Element) interface{} {
+	l.remove(e)
+	e.list = nil // do what remove does not
+	return e.Value
+}
+
+// remove the element from the list, but do not clear the Element's list field.
+// This is so that other List methods may use remove when relocating Elements
+// without needing to restore the list field.
+func (l *List) remove(e *Element) {
+	if e.list != l {
 		return
 	}
 	if e.prev == nil {
@@ -120,78 +135,59 @@ func (l *List) insertBack(e *Element) {
 
 // PushFront inserts the value at the front of the list and returns a new Element containing the value.
 func (l *List) PushFront(value interface{}) *Element {
-	if l.id == nil {
-		l.Init()
-	}
-	e := &Element{nil, nil, l.id, value}
+	e := &Element{nil, nil, l, value}
 	l.insertFront(e)
 	return e
 }
 
 // PushBack inserts the value at the back of the list and returns a new Element containing the value.
 func (l *List) PushBack(value interface{}) *Element {
-	if l.id == nil {
-		l.Init()
-	}
-	e := &Element{nil, nil, l.id, value}
+	e := &Element{nil, nil, l, value}
 	l.insertBack(e)
 	return e
 }
 
 // InsertBefore inserts the value immediately before mark and returns a new Element containing the value.
 func (l *List) InsertBefore(value interface{}, mark *Element) *Element {
-	if mark.id != l.id {
+	if mark.list != l {
 		return nil
 	}
-	e := &Element{nil, nil, l.id, value}
+	e := &Element{nil, nil, l, value}
 	l.insertBefore(e, mark)
 	return e
 }
 
 // InsertAfter inserts the value immediately after mark and returns a new Element containing the value.
 func (l *List) InsertAfter(value interface{}, mark *Element) *Element {
-	if mark.id != l.id {
+	if mark.list != l {
 		return nil
 	}
-	e := &Element{nil, nil, l.id, value}
+	e := &Element{nil, nil, l, value}
 	l.insertAfter(e, mark)
 	return e
 }
 
 // MoveToFront moves the element to the front of the list.
 func (l *List) MoveToFront(e *Element) {
-	if e.id != l.id || l.front == e {
+	if e.list != l || l.front == e {
 		return
 	}
-	l.Remove(e)
+	l.remove(e)
 	l.insertFront(e)
 }
 
 // MoveToBack moves the element to the back of the list.
 func (l *List) MoveToBack(e *Element) {
-	if e.id != l.id || l.back == e {
+	if e.list != l || l.back == e {
 		return
 	}
-	l.Remove(e)
+	l.remove(e)
 	l.insertBack(e)
 }
 
 // Len returns the number of elements in the list.
 func (l *List) Len() int { return l.len }
 
-func (l *List) iterate(c chan<- interface{}) {
-	for e := l.front; e != nil; e = e.next {
-		c <- e.Value
-	}
-	close(c)
-}
-
-func (l *List) Iter() <-chan interface{} {
-	c := make(chan interface{})
-	go l.iterate(c)
-	return c
-}
-
 // PushBackList inserts each element of ol at the back of the list.
 func (l *List) PushBackList(ol *List) {
 	last := ol.Back()
diff --git a/src/pkg/container/list/list_test.go b/src/pkg/container/list/list_test.go
index bf35c9dd9..1d44ff84e 100644
--- a/src/pkg/container/list/list_test.go
+++ b/src/pkg/container/list/list_test.go
@@ -23,8 +23,7 @@ func checkListPointers(t *testing.T, l *List, es []*Element) {
 		t.Errorf("l.back = %v, want %v", l.back, last)
 	}
 
-	for i := 0; i < len(es); i++ {
-		e := es[i]
+	for i, e := range es {
 		var e_prev, e_next *Element = nil, nil
 		if i > 0 {
 			e_prev = es[i-1]
@@ -116,8 +115,8 @@ func TestList(t *testing.T) {
 
 	// Check standard iteration.
 	sum := 0
-	for e := range l.Iter() {
-		if i, ok := e.(int); ok {
+	for e := l.Front(); e != nil; e = e.Next() {
+		if i, ok := e.Value.(int); ok {
 			sum += i
 		}
 	}
@@ -141,7 +140,8 @@ func checkList(t *testing.T, l *List, es []interface{}) {
 		return
 	}
 	i := 0
-	for le := range l.Iter() {
+	for e := l.Front(); e != nil; e = e.Next() {
+		le := e.Value.(int)
 		if le != es[i] {
 			t.Errorf("elt #%d has value=%v, want %v", i, le, es[i])
 		}
@@ -193,3 +193,17 @@ func TestExtending(t *testing.T) {
 	l1.PushFrontList(l3)
 	checkList(t, l1, []interface{}{1, 2, 3})
 }
+
+func TestRemove(t *testing.T) {
+	l := New()
+	e1 := l.PushBack(1)
+	e2 := l.PushBack(2)
+	checkListPointers(t, l, []*Element{e1, e2})
+	e := l.Front()
+	l.Remove(e)
+	checkListPointers(t, l, []*Element{e2})
+	checkListLen(t, l, 1)
+	l.Remove(e)
+	checkListPointers(t, l, []*Element{e2})
+	checkListLen(t, l, 1)
+}