diff --git a/funcs-math.go b/funcs-math.go
new file mode 100644
index 0000000..567adbd
--- /dev/null
+++ b/funcs-math.go
@@ -0,0 +1,139 @@
+// funcs-math.go
+package expr
+
+import (
+	"fmt"
+	"io"
+)
+
+// func addFunc(ctx exprContext, name string, args []any) (result any, err error) {
+// 	var sumAsFloat = false
+// 	var floatSum float64 = 0.0
+// 	var intSum int64 = 0
+
+// 	for i, v := range args {
+// 		if !isNumber(v) {
+// 			err = fmt.Errorf("add(): param nr %d has wrong type %T, number expected", i+1, v)
+// 			break
+// 		}
+
+// 		if !sumAsFloat && isFloat(v) {
+// 			sumAsFloat = true
+// 			floatSum = float64(intSum)
+// 		}
+// 		if sumAsFloat {
+// 			floatSum += numAsFloat(v)
+// 		} else {
+// 			iv, _ := v.(int64)
+// 			intSum += iv
+// 		}
+// 	}
+// 	if err == nil {
+// 		if sumAsFloat {
+// 			result = floatSum
+// 		} else {
+// 			result = intSum
+// 		}
+// 	}
+// 	return
+// }
+
+func checkNumberParamExpected(funcName string, paramValue any, paramPos int) (err error) {
+	if !(isNumber(paramValue) || isList(paramValue)) {
+		err = fmt.Errorf("%s(): param nr %d has wrong type %T, number expected", funcName, paramPos+1, paramValue)
+	}
+	return
+}
+
+func doAdd(ctx exprContext, name string, it Iterator) (result any, err error) {
+	var sumAsFloat = false
+	var floatSum float64 = 0.0
+	var intSum int64 = 0
+	var v any
+
+	for v, err = it.Next(); err == nil; v, err = it.Next() {
+		if err = checkNumberParamExpected(name, v, it.Index()); err != nil {
+			break
+		}
+
+		if array, ok := v.([]any); ok {
+			if v, err = doAdd(ctx, name, NewFlatArrayIterator(array)); err != nil {
+				break
+			}
+		}
+
+		if !sumAsFloat && isFloat(v) {
+			sumAsFloat = true
+			floatSum = float64(intSum)
+		}
+		if sumAsFloat {
+			floatSum += numAsFloat(v)
+		} else {
+			iv, _ := v.(int64)
+			intSum += iv
+		}
+	}
+	if err == nil || err == io.EOF {
+		err = nil
+		if sumAsFloat {
+			result = floatSum
+		} else {
+			result = intSum
+		}
+	}
+	return
+}
+
+func addFunc(ctx exprContext, name string, args []any) (result any, err error) {
+	result, err = doAdd(ctx, name, NewFlatArrayIterator(args))
+	return
+}
+
+func doMul(ctx exprContext, name string, it Iterator) (result any, err error) {
+	var mulAsFloat = false
+	var floatProd float64 = 1.0
+	var intProd int64 = 1
+	var v any
+
+	for v, err = it.Next(); err == nil; v, err = it.Next() {
+		if err = checkNumberParamExpected(name, v, it.Index()); err != nil {
+			break
+		}
+
+		if array, ok := v.([]any); ok {
+			if v, err = doAdd(ctx, name, NewFlatArrayIterator(array)); err != nil {
+				break
+			}
+		}
+
+		if !mulAsFloat && isFloat(v) {
+			mulAsFloat = true
+			floatProd = float64(intProd)
+		}
+		if mulAsFloat {
+			floatProd *= numAsFloat(v)
+		} else {
+			iv, _ := v.(int64)
+			intProd *= iv
+		}
+	}
+	if err == nil || err == io.EOF {
+		err = nil
+		if mulAsFloat {
+			result = floatProd
+		} else {
+			result = intProd
+		}
+	}
+	return
+}
+
+func mulFunc(ctx exprContext, name string, args []any) (result any, err error) {
+	result, err = doMul(ctx, name, NewFlatArrayIterator(args))
+	return
+}
+
+func importMathFuncs(ctx exprContext) {
+	ctx.RegisterFunc("add", addFunc, 0, -1)
+	ctx.RegisterFunc("mul", mulFunc, 0, -1)
+}