Iterators now support generic operation interface based on methods HasOperation() and CallOperation().

Also fixed mul() function that called doAdd() instead of doMul().

data-cursor.go

@@ -18,7 +18,7 @@ const (
 )
 
 type dataCursor struct {
-	ds          map[any]*term
+	ds          map[string]Functor
 	ctx         ExprContext
 	index       int
 	resource    any
@@ -28,8 +28,9 @@ type dataCursor struct {
 	currentFunc Functor
 }
 
-func newDataCursor(ctx ExprContext) (dc *dataCursor) {
+func newDataCursor(ctx ExprContext, ds map[string]Functor) (dc *dataCursor) {
 	dc = &dataCursor{
+		ds:    ds,
 		index: -1,
 		ctx:   ctx.Clone(),
 	}
@@ -40,6 +41,24 @@ func (dc *dataCursor) String() string {
 	return "$(...)"
 }
 
+func (dc *dataCursor) HasOperation(name string) (exists bool) {
+	f, ok := dc.ds[name]
+	exists = ok && isFunctor(f)
+	return
+}
+
+func (dc *dataCursor) CallOperation(name string) (value any, err error) {
+	if functor, ok := dc.ds[name]; ok && isFunctor(functor) {
+		ctx := cloneContext(dc.ctx)
+		value, err = functor.Invoke(ctx, name, []any{})
+		exportObjects(dc.ctx, ctx)
+
+	} else {
+		err = errNoOperation(name)
+	}
+	return
+}
+
 func (dc *dataCursor) Reset() (err error) {
 	if dc.resetFunc != nil {
 		ctx := cloneContext(dc.ctx)