Implemented (but not tested) cursor.RuneReader

cursor/cursor.go

@@ -25,6 +25,9 @@ type Cursor[Datum any] interface {
 
 	// Pos returns the Cursor's position within the source.
 	Pos() uint64
+
+	// At returns a new cursor at the position pos.
+	At(pos uint64) Cursor[Datum]
 }
 
 type SliceCursor[Datum any] struct {
@@ -56,6 +59,11 @@ func (sc SliceCursor[Datum]) Pos() uint64 {
 	return sc.offset
 }
 
+func (sc SliceCursor[Datum]) At(pos uint64) Cursor[Datum] {
+	sc.offset = pos
+	return sc
+}
+
 type ReaderAtCursor struct {
 	r   io.ReaderAt
 	pos uint64
@@ -77,6 +85,11 @@ func (rac ReaderAtCursor) Pos() uint64 {
 	return rac.pos
 }
 
+func (rac ReaderAtCursor) At(pos uint64) Cursor[byte] {
+	rac.pos = pos
+	return rac
+}
+
 // StringCursor is identical to SliceCursor[byte], but uses a string as its data source.
 // The advantage is that creating a StringCursor does not require copying the source
 // string into a []byte.
@@ -105,3 +118,8 @@ func (sc StringCursor) Read(dst []byte) (n uint64, next Cursor[byte], err error)
 func (sc StringCursor) Pos() uint64 {
 	return sc.offset
 }
+
+func (sc StringCursor) At(pos uint64) Cursor[byte] {
+	sc.offset = pos
+	return sc
+}