diff --git a/data-cursor.go b/data-cursor.go
index ea72d66..cff0c0d 100644
--- a/data-cursor.go
+++ b/data-cursor.go
@@ -85,7 +85,7 @@ func (dc *dataCursor) HasOperation(name string) (exists bool) {
 	return
 }
 
-func (dc *dataCursor) CallOperation(name string, args []any) (value any, err error) {
+func (dc *dataCursor) CallOperation(name string, args map[string]any) (value any, err error) {
 	if name == IndexName {
 		value = int64(dc.Index())
 	} else if functor, ok := dc.ds[name]; ok && isFunctor(functor) {
@@ -95,7 +95,7 @@ func (dc *dataCursor) CallOperation(name string, args []any) (value any, err err
 			value, err = dc.Reset()
 		} else {
 			ctx := cloneContext(dc.ctx)
-			value, err = functor.InvokeNamed(ctx, name, map[string]any{})
+			value, err = functor.InvokeNamed(ctx, name, args)
 			exportObjects(dc.ctx, ctx)
 		}
 	} else {
@@ -239,16 +239,3 @@ func (dc *dataCursor) Count() int {
 	return dc.count
 }
 
-
-func buildActualParams(functor Functor, args []any) (actualParams map[string]any) {
-	formalParams := functor.GetParams()
-	actualParams = make(map[string]any, len(formalParams))
-	for i, spec := range formalParams {
-		if i < len(formalParams) {
-			actualParams[spec.Name()] = args[i]
-		} else {
-			actualParams[spec.Name()] = nil
-		}
-	}
-	return
-}
diff --git a/function.go b/function.go
index 3f8dbaf..c0a29bf 100644
--- a/function.go
+++ b/function.go
@@ -6,6 +6,7 @@ package expr
 
 import (
 	"fmt"
+	"strconv"
 	"strings"
 )
 
@@ -223,13 +224,17 @@ func (info *funcInfo) checkExistingParam(paramName string) (exists bool) {
 	return
 }
 
-func (info *funcInfo) initActualParams(ctx ExprContext, name string, callTerm *term) (params map[string]any, err error) {
+func (info *funcInfo) initActualParams(ctx ExprContext, name string, callTerm *term) (actualParams map[string]any, err error) {
 	var varArgs []any
 	var varName string
 
 	namedParamsStarted := false
 
-	actualParams := make(map[string]any, len(info.formalParams))
+	actualParams = make(map[string]any, len(info.formalParams))
+	if callTerm == nil {
+		return
+	}
+
 	for i, tree := range callTerm.children {
 		var paramValue any
 		paramCtx := ctx.Clone()
@@ -268,7 +273,6 @@ func (info *funcInfo) initActualParams(ctx ExprContext, name string, callTerm *t
 		if varArgs != nil {
 			actualParams[varName] = varArgs
 		}
-		params = actualParams
 	}
 	return
 }
@@ -319,7 +323,7 @@ func getAssignVarName(t *term) (name string, ok bool) {
 	return
 }
 
-func CallFunction3(parentCtx ExprContext, name string, callTerm *term) (result any, err error) {
+func CallFunction(parentCtx ExprContext, name string, callTerm *term) (result any, err error) {
 	var actualParams map[string]any
 	if info, exists := GetFuncInfo(parentCtx, name); exists {
 		var ctx ExprContext
@@ -333,3 +337,25 @@ func CallFunction3(parentCtx ExprContext, name string, callTerm *term) (result a
 	}
 	return
 }
+
+func GetParam(args map[string]any, paramName string, paramNum int) (value any, exists bool) {
+	if value, exists = args[paramName]; !exists {
+		if paramNum > 0 && paramNum <= len(args) {
+			value, exists = args["arg"+strconv.Itoa(paramNum)]
+		}
+	}
+	return
+}
+
+func buildActualParams(functor Functor, args []any) (actualParams map[string]any) {
+	formalParams := functor.GetParams()
+	actualParams = make(map[string]any, len(args))
+	for i, arg := range args {
+		if i < len(formalParams) {
+			actualParams[formalParams[i].Name()] = arg
+		} else {
+			actualParams["arg"+strconv.Itoa(i+1)] = arg
+		}
+	}
+	return
+}