Implement string-lenght-limit like the game

pkg/vm/operations.go

@@ -3,10 +3,13 @@ package vm
 import (
 	"fmt"
 	"strings"
+	"unicode/utf8"
 
 	"github.com/dbaumgarten/yodk/pkg/number"
 )
 
+const MaxStringLenght = 1024
+
 // RunUnaryOperation executes the given operation with the given argument and returns the result
 func RunUnaryOperation(arg *Variable, operator string) (*Variable, error) {
 	var result Variable
@@ -178,7 +181,13 @@ func RunBinaryOperation(arg1 *Variable, arg2 *Variable, operator string) (*Varia
 	if arg1.IsString() {
 		switch operator {
 		case "+":
-			endResult.Value = arg1.String() + arg2.String()
+			value := arg1.String() + arg2.String()
+			size := utf8.RuneCountInString(value)
+			if size > MaxStringLenght {
+				runes := []rune(value)
+				value = string(runes[:1024])
+			}
+			endResult.Value = value
 			break
 		case "-":
 			lastIndex := strings.LastIndex(arg1.String(), arg2.String())

pkg/vm/vm.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strings"
 	"sync"
+	"unicode/utf8"
 
 	"github.com/dbaumgarten/yodk/pkg/number"
 	"github.com/dbaumgarten/yodk/pkg/parser"
@@ -708,13 +709,20 @@ func (v *VM) runDeref(d *ast.Dereference) (*Variable, error) {
 		case "":
 			return oldval, nil
 		case "++":
-			newval.Value = oldval.String() + " "
+			if len(oldval.String()) < MaxStringLenght {
+				newval.Value = oldval.String() + " "
+			}
 			break
 		case "--":
-			if len(oldval.String()) == 0 {
+			str := oldval.String()
+			if len(str) == 0 {
 				return nil, RuntimeError{fmt.Errorf("String in variable '%s' is already empty", d.Variable), d}
 			}
-			newval.Value = string([]rune(oldval.String())[:len(oldval.String())-1])
+			r, size := utf8.DecodeLastRuneInString(str)
+			if r == utf8.RuneError && (size == 0 || size == 1) {
+				size = 0
+			}
+			newval.Value = str[:len(str)-size]
 			break
 		default:
 			return nil, RuntimeError{fmt.Errorf("Unknown operator '%s'", d.Operator), d}