使用LR分析算法跟蹤移進/歸約沖突和歸約/歸約沖突是件樂在其中的事。為了輔助調試，yacc.py在生成分析表時會創建出一個調試文件叫parser.out： ~~~ Unused terminals: Grammar Rule 1 expression -> expression PLUS expression Rule 2 expression -> expression MINUS expression Rule 3 expression -> expression TIMES expression Rule 4 expression -> expression DIVIDE expression Rule 5 expression -> NUMBER Rule 6 expression -> LPAREN expression RPAREN Terminals, with rules where they appear TIMES : 3 error : MINUS : 2 RPAREN : 6 LPAREN : 6 DIVIDE : 4 PLUS : 1 NUMBER : 5 Nonterminals, with rules where they appear expression : 1 1 2 2 3 3 4 4 6 0 Parsing method: LALR state 0 S' -> . expression expression -> . expression PLUS expression expression -> . expression MINUS expression expression -> . expression TIMES expression expression -> . expression DIVIDE expression expression -> . NUMBER expression -> . LPAREN expression RPAREN NUMBER shift and go to state 3 LPAREN shift and go to state 2 state 1 S' -> expression . expression -> expression . PLUS expression expression -> expression . MINUS expression expression -> expression . TIMES expression expression -> expression . DIVIDE expression PLUS shift and go to state 6 MINUS shift and go to state 5 TIMES shift and go to state 4 DIVIDE shift and go to state 7 state 2 expression -> LPAREN . expression RPAREN expression -> . expression PLUS expression expression -> . expression MINUS expression expression -> . expression TIMES expression expression -> . expression DIVIDE expression expression -> . NUMBER expression -> . LPAREN expression RPAREN NUMBER shift and go to state 3 LPAREN shift and go to state 2 state 3 expression -> NUMBER . $ reduce using rule 5 PLUS reduce using rule 5 MINUS reduce using rule 5 TIMES reduce using rule 5 DIVIDE reduce using rule 5 RPAREN reduce using rule 5 state 4 expression -> expression TIMES . expression expression -> . expression PLUS expression expression -> . expression MINUS expression expression -> . expression TIMES expression expression -> . expression DIVIDE expression expression -> . NUMBER expression -> . LPAREN expression RPAREN NUMBER shift and go to state 3 LPAREN shift and go to state 2 state 5 expression -> expression MINUS . expression expression -> . expression PLUS expression expression -> . expression MINUS expression expression -> . expression TIMES expression expression -> . expression DIVIDE expression expression -> . NUMBER expression -> . LPAREN expression RPAREN NUMBER shift and go to state 3 LPAREN shift and go to state 2 state 6 expression -> expression PLUS . expression expression -> . expression PLUS expression expression -> . expression MINUS expression expression -> . expression TIMES expression expression -> . expression DIVIDE expression expression -> . NUMBER expression -> . LPAREN expression RPAREN NUMBER shift and go to state 3 LPAREN shift and go to state 2 state 7 expression -> expression DIVIDE . expression expression -> . expression PLUS expression expression -> . expression MINUS expression expression -> . expression TIMES expression expression -> . expression DIVIDE expression expression -> . NUMBER expression -> . LPAREN expression RPAREN NUMBER shift and go to state 3 LPAREN shift and go to state 2 state 8 expression -> LPAREN expression . RPAREN expression -> expression . PLUS expression expression -> expression . MINUS expression expression -> expression . TIMES expression expression -> expression . DIVIDE expression RPAREN shift and go to state 13 PLUS shift and go to state 6 MINUS shift and go to state 5 TIMES shift and go to state 4 DIVIDE shift and go to state 7 state 9 expression -> expression TIMES expression . expression -> expression . PLUS expression expression -> expression . MINUS expression expression -> expression . TIMES expression expression -> expression . DIVIDE expression $ reduce using rule 3 PLUS reduce using rule 3 MINUS reduce using rule 3 TIMES reduce using rule 3 DIVIDE reduce using rule 3 RPAREN reduce using rule 3 ! PLUS [ shift and go to state 6 ] ! MINUS [ shift and go to state 5 ] ! TIMES [ shift and go to state 4 ] ! DIVIDE [ shift and go to state 7 ] state 10 expression -> expression MINUS expression . expression -> expression . PLUS expression expression -> expression . MINUS expression expression -> expression . TIMES expression expression -> expression . DIVIDE expression $ reduce using rule 2 PLUS reduce using rule 2 MINUS reduce using rule 2 RPAREN reduce using rule 2 TIMES shift and go to state 4 DIVIDE shift and go to state 7 ! TIMES [ reduce using rule 2 ] ! DIVIDE [ reduce using rule 2 ] ! PLUS [ shift and go to state 6 ] ! MINUS [ shift and go to state 5 ] state 11 expression -> expression PLUS expression . expression -> expression . PLUS expression expression -> expression . MINUS expression expression -> expression . TIMES expression expression -> expression . DIVIDE expression $ reduce using rule 1 PLUS reduce using rule 1 MINUS reduce using rule 1 RPAREN reduce using rule 1 TIMES shift and go to state 4 DIVIDE shift and go to state 7 ! TIMES [ reduce using rule 1 ] ! DIVIDE [ reduce using rule 1 ] ! PLUS [ shift and go to state 6 ] ! MINUS [ shift and go to state 5 ] state 12 expression -> expression DIVIDE expression . expression -> expression . PLUS expression expression -> expression . MINUS expression expression -> expression . TIMES expression expression -> expression . DIVIDE expression $ reduce using rule 4 PLUS reduce using rule 4 MINUS reduce using rule 4 TIMES reduce using rule 4 DIVIDE reduce using rule 4 RPAREN reduce using rule 4 ! PLUS [ shift and go to state 6 ] ! MINUS [ shift and go to state 5 ] ! TIMES [ shift and go to state 4 ] ! DIVIDE [ shift and go to state 7 ] state 13 expression -> LPAREN expression RPAREN . $ reduce using rule 6 PLUS reduce using rule 6 MINUS reduce using rule 6 TIMES reduce using rule 6 DIVIDE reduce using rule 6 RPAREN reduce using rule 6 ~~~ 文件中出現的不同狀態，代表了有效輸入標記的所有可能的組合，這是依據文法規則得到的。當得到輸入標記時，分析器將構造一個棧，并找到匹配的規則。每個狀態跟蹤了當前輸入進行到語法規則中的哪個位置，在每個規則中，’.’表示當前分析到規則的哪個位置，而且，對于在當前狀態下，輸入的每個有效標記導致的動作也被羅列出來。當出現移進/歸約或歸約/歸約沖突時，被忽略的規則前面會添加!，就像這樣： ~~~ ! TIMES [ reduce using rule 2 ] ! DIVIDE [ reduce using rule 2 ] ! PLUS [ shift and go to state 6 ] ! MINUS [ shift and go to state 5 ] ~~~ 通過查看這些規則并結合一些實例，通常能夠找到大部分沖突的根源。應該強調的是，不是所有的移進歸約沖突都是不好的，想要確定解決方法是否正確，唯一的辦法就是查看parser.out。