我正在使用CUP和JFlex來驗證表達式語法。我有基本的功能工作:我可以告訴表達式是否有效。使用Java CUP解析樹生成
下一步是執行簡單的算術運算,如「加1」。例如,如果我的表達式是「1 + a」,結果應該是「2 + a」。我需要訪問解析樹來做到這一點,因爲只需標識數字項就不會這樣做:將「(1 + a)* b」加1的結果應該是「(1 + a)* b + 1」 ,而不是「(2 + a)* b」。
有沒有人有一個生成分析樹的CUP示例?我想我可以從那裏拿走它。
作爲額外的好處,是否有一種方法可以使用JFlex獲取表達式中所有令牌的列表?看起來像一個典型的用例,但我無法弄清楚如何去做。
編輯:實測值上堆棧溢出一個有前途的線索:CUP的 Create abstract tree problem from parser
討論和AST:
http://pages.cs.wisc.edu/~fischer/cs536.s08/lectures/Lecture16.4up.pdf
具體而言,本段:
象徵解析器返回的內容與語法的開始0相關聯符號幷包含整個源程序的AST
這沒有幫助。如何遍歷給定的樹Symbol實例,如果Symbol類沒有任何導航指針給它的子元素?換句話說,它看起來或行爲不像樹節點:
package java_cup.runtime;
/**
* Defines the Symbol class, which is used to represent all terminals
* and nonterminals while parsing. The lexer should pass CUP Symbols
* and CUP returns a Symbol.
*
* @version last updated: 7/3/96
* @author Frank Flannery
*/
/* ****************************************************************
Class Symbol
what the parser expects to receive from the lexer.
the token is identified as follows:
sym: the symbol type
parse_state: the parse state.
value: is the lexical value of type Object
left : is the left position in the original input file
right: is the right position in the original input file
******************************************************************/
public class Symbol {
/*******************************
Constructor for l,r values
*******************************/
public Symbol(int id, int l, int r, Object o) {
this(id);
left = l;
right = r;
value = o;
}
/*******************************
Constructor for no l,r values
********************************/
public Symbol(int id, Object o) {
this(id, -1, -1, o);
}
/*****************************
Constructor for no value
***************************/
public Symbol(int id, int l, int r) {
this(id, l, r, null);
}
/***********************************
Constructor for no value or l,r
***********************************/
public Symbol(int sym_num) {
this(sym_num, -1);
left = -1;
right = -1;
value = null;
}
/***********************************
Constructor to give a start state
***********************************/
Symbol(int sym_num, int state)
{
sym = sym_num;
parse_state = state;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** The symbol number of the terminal or non terminal being represented */
public int sym;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** The parse state to be recorded on the parse stack with this symbol.
* This field is for the convenience of the parser and shouldn't be
* modified except by the parser.
*/
public int parse_state;
/** This allows us to catch some errors caused by scanners recycling
* symbols. For the use of the parser only. [CSA, 23-Jul-1999] */
boolean used_by_parser = false;
/*******************************
The data passed to parser
*******************************/
public int left, right;
public Object value;
/*****************************
Printing this token out. (Override for pretty-print).
****************************/
public String toString() { return "#"+sym; }
}