Merge pull request #86 from tylertreat-wf/ctrie

Ctrie

Author: dustinhiatt-wf

list/persistent.go

@@ -0,0 +1,239 @@
+/*
+Copyright 2015 Workiva, LLC
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/*
+Package list provides list implementations. Currently, this includes a
+persistent, immutable linked list.
+*/
+package list
+
+import "errors"
+
+var (
+	// Empty is an empty PersistentList.
+	Empty PersistentList = &emptyList{}
+
+	// ErrEmptyList is returned when an invalid operation is performed on an
+	// empty list.
+	ErrEmptyList = errors.New("Empty list")
+)
+
+// PersistentList is an immutable, persistent linked list.
+type PersistentList interface {
+	// Head returns the head of the list. The bool will be false if the list is
+	// empty.
+	Head() (interface{}, bool)
+
+	// Tail returns the tail of the list. The bool will be false if the list is
+	// empty.
+	Tail() (PersistentList, bool)
+
+	// IsEmpty indicates if the list is empty.
+	IsEmpty() bool
+
+	// Length returns the number of items in the list.
+	Length() uint
+
+	// Add will add the item to the list, returning the new list.
+	Add(head interface{}) PersistentList
+
+	// Insert will insert the item at the given position, returning the new
+	// list or an error if the position is invalid.
+	Insert(val interface{}, pos uint) (PersistentList, error)
+
+	// Get returns the item at the given position or an error if the position
+	// is invalid.
+	Get(pos uint) (interface{}, bool)
+
+	// Remove will remove the item at the given position, returning the new
+	// list or an error if the position is invalid.
+	Remove(pos uint) (PersistentList, error)
+
+	// Find applies the predicate function to the list and returns the first
+	// item which matches.
+	Find(func(interface{}) bool) (interface{}, bool)
+
+	// FindIndex applies the predicate function to the list and returns the
+	// index of the first item which matches or -1 if there is no match.
+	FindIndex(func(interface{}) bool) int
+}
+
+type emptyList struct{}
+
+// Head returns the head of the list. The bool will be false if the list is
+// empty.
+func (e *emptyList) Head() (interface{}, bool) {
+	return nil, false
+}
+
+// Tail returns the tail of the list. The bool will be false if the list is
+// empty.
+func (e *emptyList) Tail() (PersistentList, bool) {
+	return nil, false
+}
+
+// IsEmpty indicates if the list is empty.
+func (e *emptyList) IsEmpty() bool {
+	return true
+}
+
+// Length returns the number of items in the list.
+func (e *emptyList) Length() uint {
+	return 0
+}
+
+// Add will add the item to the list, returning the new list.
+func (e *emptyList) Add(head interface{}) PersistentList {
+	return &list{head, e}
+}
+
+// Insert will insert the item at the given position, returning the new list or
+// an error if the position is invalid.
+func (e *emptyList) Insert(val interface{}, pos uint) (PersistentList, error) {
+	if pos == 0 {
+		return e.Add(val), nil
+	}
+	return nil, ErrEmptyList
+}
+
+// Get returns the item at the given position or an error if the position is
+// invalid.
+func (e *emptyList) Get(pos uint) (interface{}, bool) {
+	return nil, false
+}
+
+// Remove will remove the item at the given position, returning the new list or
+// an error if the position is invalid.
+func (e *emptyList) Remove(pos uint) (PersistentList, error) {
+	return nil, ErrEmptyList
+}
+
+// Find applies the predicate function to the list and returns the first item
+// which matches.
+func (e *emptyList) Find(func(interface{}) bool) (interface{}, bool) {
+	return nil, false
+}
+
+// FindIndex applies the predicate function to the list and returns the index
+// of the first item which matches or -1 if there is no match.
+func (e *emptyList) FindIndex(func(interface{}) bool) int {
+	return -1
+}
+
+type list struct {
+	head interface{}
+	tail PersistentList
+}
+
+// Head returns the head of the list. The bool will be false if the list is
+// empty.
+func (l *list) Head() (interface{}, bool) {
+	return l.head, true
+}
+
+// Tail returns the tail of the list. The bool will be false if the list is
+// empty.
+func (l *list) Tail() (PersistentList, bool) {
+	return l.tail, true
+}
+
+// IsEmpty indicates if the list is empty.
+func (l *list) IsEmpty() bool {
+	return false
+}
+
+// Length returns the number of items in the list.
+func (l *list) Length() uint {
+	curr := l
+	length := uint(0)
+	for {
+		length += 1
+		tail, _ := curr.Tail()
+		if tail.IsEmpty() {
+			return length
+		}
+		curr = tail.(*list)
+	}
+}
+
+// Add will add the item to the list, returning the new list.
+func (l *list) Add(head interface{}) PersistentList {
+	return &list{head, l}
+}
+
+// Insert will insert the item at the given position, returning the new list or
+// an error if the position is invalid.
+func (l *list) Insert(val interface{}, pos uint) (PersistentList, error) {
+	if pos == 0 {
+		return l.Add(val), nil
+	}
+	nl, err := l.tail.Insert(val, pos-1)
+	if err != nil {
+		return nil, err
+	}
+	return nl.Add(l.head), nil
+}
+
+// Get returns the item at the given position or an error if the position is
+// invalid.
+func (l *list) Get(pos uint) (interface{}, bool) {
+	if pos == 0 {
+		return l.head, true
+	}
+	return l.tail.Get(pos - 1)
+}
+
+// Remove will remove the item at the given position, returning the new list or
+// an error if the position is invalid.
+func (l *list) Remove(pos uint) (PersistentList, error) {
+	if pos == 0 {
+		nl, _ := l.Tail()
+		return nl, nil
+	}
+
+	nl, err := l.tail.Remove(pos - 1)
+	if err != nil {
+		return nil, err
+	}
+	return &list{l.head, nl}, nil
+}
+
+// Find applies the predicate function to the list and returns the first item
+// which matches.
+func (l *list) Find(pred func(interface{}) bool) (interface{}, bool) {
+	if pred(l.head) {
+		return l.head, true
+	}
+	return l.tail.Find(pred)
+}
+
+// FindIndex applies the predicate function to the list and returns the index
+// of the first item which matches or -1 if there is no match.
+func (l *list) FindIndex(pred func(interface{}) bool) int {
+	curr := l
+	idx := 0
+	for {
+		if pred(curr.head) {
+			return idx
+		}
+		tail, _ := curr.Tail()
+		if tail.IsEmpty() {
+			return -1
+		}
+		curr = tail.(*list)
+		idx += 1
+	}
+}