add exit() builtin

Signed-off-by: Flipez <code@brauser.io>

evaluator/builtins.go

@@ -3,6 +3,7 @@ package evaluator
 import (
 	"fmt"
 	"github.com/flipez/rocket-lang/object"
+	"os"
 )
 
 var builtins = map[string]*object.Builtin{
@@ -125,6 +126,20 @@ var builtins = map[string]*object.Builtin{
 				fmt.Println(arg.Inspect())
 			}
 
+			return NULL
+		},
+	},
+	"exit": &object.Builtin{
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1", len(args))
+			}
+			if args[0].Type() != object.INTEGER_OBJ {
+				return newError("argument to `exit` must be INTEGER, got=%s", args[0].Type())
+			}
+
+			os.Exit(int(args[0].(*object.Integer).Value))
+
 			return NULL
 		},
 	},