From 3ee6675e72841dc88331a0e11345c6abd3fa9fb1 Mon Sep 17 00:00:00 2001
From: Kagura <me@kagurach.uk>
Date: Wed, 19 Jun 2024 21:03:45 +0800
Subject: [PATCH] Add remove left recusive

---
 LL1/src/AnalyzeTable.kt | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/LL1/src/AnalyzeTable.kt b/LL1/src/AnalyzeTable.kt
index f22ef5b..dee0b25 100644
--- a/LL1/src/AnalyzeTable.kt
+++ b/LL1/src/AnalyzeTable.kt
@@ -13,25 +13,40 @@ class AnalyzeTable {
 
     constructor() : this(
         """
-        E  ::= TE'
-        E' -> +TE'|ε
-        T  -> FT'
-        T' ::= *FT'|ε
-        F  -> (E)|i
+        E->E+T|T
+        T->T*F|F
+        F->(E)|i
     """.trimIndent()
     )
 
     constructor(lang: String, _s: String? = null) {
         start = _s ?: lang.trim()[0].toString()
 
-        val lang = if ("::=" in lang) { // 换成一个符号方便
+        val newLang = if ("::=" in lang) { // 换成一个符号方便
             lang.replace("::=", "->")
         } else {
             lang
         }
 
+        // 检查并消除左递归
+        var noLeftRecLang = ""
+        for (line in newLang.split("\n")) {
+            val l = line.split("->")[0]
+            val r = line.split("->")[1]
+
+            if (r.startsWith(l)){
+                val rec = r.split("|", limit = 2)[0].substring(l.length)
+                val rest = r.split("|", limit = 2)[1]
+                noLeftRecLang += "$l->$rest$l'\n" +
+                        "$l'->$rec$l'|$NULL\n"
+            }else{
+                noLeftRecLang += line
+            }
+
+        }
+
         // 先拆分
-        lang.split("\n").forEach { s ->
+        noLeftRecLang.split("\n").forEach { s ->
             val vn = s.split("->")[0].trim()
             if (vn.isNotEmpty() && !V_n.contains(vn)) {
                 V_n.add(vn)