完善注释，修正获取头尾元素的逻辑

src/Reader/FileReader.php

@@ -15,8 +15,8 @@ class FileReader extends StringReader
 {
     /**
      * FileReader constructor.
-     * @param string $fileName
-     * @throws FileNotFoundException
+     * @param string $fileName 文件名
+     * @throws FileNotFoundException 文件不存在时报错
      * @author Jerry Yan <792602257@qq.com>
      * @date 2021/1/26 13:52
      */

src/Token/TokenInterface.php

@@ -38,19 +38,23 @@ abstract class TokenInterface
 
     /**
      * 获取链表第一个元素
-     * @return ?$this
+     * @return $this
      * @author Jerry Yan <792602257@qq.com>
      * @date 2021/1/22 10:01
      */
-    public function getFirstToken(): ?TokenInterface
+    public function getFirstToken(): TokenInterface
     {
-        if ($this->hasPrevToken()) return $this->getPrevToken()->getFirstToken();
-        else return $this;
+        return $this->hasPrevToken() ? $this->getPrevToken()->getFirstToken() : $this;
     }
-    public function getLastToken(): ?TokenInterface
+    /**
+     * 获取链表最后一个元素
+     * @return $this
+     * @author Jerry Yan <792602257@qq.com>
+     * @date 2021/2/19 11:05
+     */
+    public function getLastToken(): TokenInterface
     {
-        if ($this->hasNextToken()) return $this->getNextToken()->getLastToken();
-        else return $this;
+        return $this->hasNextToken() ? $this->getNextToken()->getLastToken() : $this;
     }
     public function hasPrevToken(): bool
     {
@@ -84,4 +88,8 @@ abstract class TokenInterface
     {
         return $this->getLength();
     }
+    public function getRawString(): string
+    {
+        return $this->_raw;
+    }
 }

src/Token/TokenType.php

@@ -1,21 +0,0 @@
-<?php
-/**
- * @filename TokenType.php
- * @author Jerry Yan <792602257@qq.com>
- * @date 2020/12/17 15:04
- */
-
-
-namespace JerryYan\DSL\Token;
-
-
-/**
- * Token分类Enum
- * @package JerryYan\DSL\Token
- * @author Jerry Yan <792602257@qq.com>
- * @date 2020/12/17 15:04
- */
-final class TokenType
-{
-
-}