diff --git a/builtin-base.go b/builtin-base.go
index b57a4b9..91e5631 100644
--- a/builtin-base.go
+++ b/builtin-base.go
@@ -5,6 +5,7 @@
 package expr
 
 import (
+	"fmt"
 	"math"
 	"strconv"
 )
@@ -120,6 +121,32 @@ func decFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	return
 }
 
+func stringFunc(ctx ExprContext, name string, args []any) (result any, err error) {
+	switch v := args[0].(type) {
+	case int64:
+		result = strconv.FormatInt(v, 10)
+	case float64:
+		result = strconv.FormatFloat(v, 'g', -1, 64)
+	case bool:
+		if v {
+			result = "true"
+		} else {
+			result = "false"
+		}
+	case string:
+		result = v
+	case *FractionType:
+		result = v.ToString(0)
+	case Formatter:
+		result = v.ToString(0)
+	case fmt.Stringer:
+		result = v.String()
+	default:
+		err = ErrCantConvert(name, v, "string")
+	}
+	return
+}
+
 func fractFunc(ctx ExprContext, name string, args []any) (result any, err error) {
 	switch v := args[0].(type) {
 	case int64:
@@ -175,6 +202,7 @@ func ImportBuiltinsFuncs(ctx ExprContext) {
 	ctx.RegisterFunc("bool", NewGolangFunctor(boolFunc), TypeBoolean, anyParams)
 	ctx.RegisterFunc("int", NewGolangFunctor(intFunc), TypeInt, anyParams)
 	ctx.RegisterFunc("dec", NewGolangFunctor(decFunc), TypeFloat, anyParams)
+	ctx.RegisterFunc("string", NewGolangFunctor(stringFunc), TypeString, anyParams)
 	ctx.RegisterFunc("fract", NewGolangFunctor(fractFunc), TypeFraction, []ExprFuncParam{
 		NewFuncParam(ParamValue),
 		NewFuncParamFlagDef("denominator", PfDefault, 1),