feat: better recursive descent

pkg/iterator/iterator.go

@@ -7,13 +7,13 @@ import "fmt"
 
 // An iterator over slices.
 type Iterator[T any] struct {
-	data  []T
+	items []T
 	index int
 }
 
 // Create a new iterator, over a set of items.
-func New[T any](items []T) *Iterator[T] {
-	return &Iterator[T]{data: items, index: 0}
+func Of[T any](items []T) *Iterator[T] {
+	return &Iterator[T]{items: items, index: 0}
 }
 
 // Returns the current position of the iterator.
@@ -21,50 +21,40 @@ func (i Iterator[T]) Index() int {
 	return i.index
 }
 
-// Returns true if the iterator has no more items to iterate over.
-func (i Iterator[T]) IsDone() bool {
-	return i.index == len(i.data)
+func (i Iterator[T]) Copy() *Iterator[T] {
+	return &Iterator[T]{items: i.items, index: i.index}
 }
 
-// Gets the next item in the slice, if one exists. Returns an error if there
-// isn't one.
-func (i Iterator[T]) Peek() (T, error) {
-	var null T
+func (i *Iterator[T]) Sync(o *Iterator[T]) {
+	i.index = o.index
+}
 
-	if i.IsDone() {
+// Create a new iterator, over a set of items.
+func (i Iterator[T]) Get() (T, error) {
+	var null T
+	if i.Done() {
 		return null, fmt.Errorf("iterator is exhausted")
 	}
 
-	return i.data[i.index], nil
+	return i.items[i.index], nil
 }
 
-// Moves the iterator pointer to the next item. Returns the current item. Fails
-// if there are no more items to iterate over.
-func (i *Iterator[T]) Pop() (T, error) {
-	val, err := i.Peek()
-	if err != nil {
-		return val, err
+// Create a new iterator, over a set of items.
+func (i *Iterator[T]) Next() (T, error) {
+	item, err := i.Get()
+	if err == nil {
+		i.index++
 	}
 
-	i.index++
-	return val, nil
+	return item, err
 }
 
-// Pop until the clause returns false.
-func (i *Iterator[T]) PopWhile(fn func(T) bool) []T {
-	result := []T{}
-
-	for {
-		popped, err := i.Peek()
-		if err != nil || !fn(popped) {
-			break
-		}
-
-		result = append(result, popped)
-		if _, err := i.Pop(); err != nil {
-			break
-		}
-	}
-
-	return result
+// Create a new iterator, over a set of items.
+func (i *Iterator[T]) Back() {
+	i.index = max(i.index-1, 0)
+}
+
+// Returns the current position of the iterator.
+func (i Iterator[T]) Done() bool {
+	return i.index == len(i.items)
 }