add string at func, fix string split

core/values.go

@@ -3,9 +3,9 @@ package core
 import (
 	"errors"
 	"fmt"
+	"math"
 	"reflect"
 	"strconv"
-	"strings"
 )
 
 type ValueType int
@@ -326,17 +326,19 @@ var StringPrototype = map[string]*BuiltinFunctionValue{
 			str := this.(*StringValue).String()
 			sep := v[0].(*StringValue).String()
 
+			prev := 0
 			var out []Value
-			tmp := strings.Builder{}
-			for i := 0; i < len(str)-len(sep); i++ {
-				tmp.WriteRune([]rune(str)[i])
-
+			for i := 1; i < len(str)-len(sep); i++ {
 				if str[i:i+len(sep)] == sep {
-					out = append(out, &StringValue{tmp.String()})
-					tmp.Reset()
+					out = append(out, &StringValue{str[prev:i]})
+					prev = i + len(sep)
 				}
 			}
 
+			if prev != len(str) {
+				out = append(out, &StringValue{str[prev:len(str)]})
+			}
+
 			return &ListValue{out}, nil
 		},
 		nil,
@@ -352,6 +354,22 @@ var StringPrototype = map[string]*BuiltinFunctionValue{
 			return GoToValue(len(this.(*StringValue).Text)), nil
 		},
 	},
+	"at": {
+		Name: "at",
+		Signature: &FunctionSignature{
+			[]TypeSignature{&NumberSignature{}},
+			&StringSignature{},
+		},
+		F: func(vm *VM, this Value, args []Value) (Value, error) {
+			i := int(math.Floor(args[0].(*NumberValue).Number))
+
+			if i < 0 || i >= len(this.(*StringValue).Text) {
+				return nil, errors.New("index is out of range")
+			}
+
+			return GoToValue(string(this.(*StringValue).Text[i])), nil
+		},
+	},
 }
 
 func (v *StringValue) Get(key string) (Value, error) {