我試圖得到:(20 +(-3))* 3 /(20/3)/ 2等於4,現在,它等於17YACC語法:運算符優先級問題
所以基本上(20/3),然後除以2,然後除以[(20/3)/ 2],然後乘以17.不知道如何改變我的語法/規則/優先順序讓它正確讀取。任何指導將不勝感激,謝謝。
%%
start: PROGRAMtoken IDtoken IStoken compoundstatement
compoundstatement: BEGINtoken {print_header();} statement semi ENDtoken {print_end();}
semi: SEMItoken statement semi
|
statement: IDtoken EQtoken exp
{ regs[$1] = $3; }
| PRINTtoken exp
{ cout << $2 << endl; }
| declaration
declaration: VARtoken IDtoken comma
comma: COMMAtoken IDtoken comma
|
exp: exp PLUStoken term
{ $$ = $1 + $3; }
| exp MINUStoken term
{ $$ = $1 - $3; }
| term
{ $$ = $1; }
| MINUStoken term
{ $$ = -$2;}
term: factor
{ $$ = $1;
}
| factor TIMEStoken term
{$$ = $1 * $3;
}
| factor DIVIDEtoken term
{ $$ = $1/$3;
}
factor: ICONSTtoken
{ $$ = $1;}
| IDtoken
{ $$ = regs[$1]; }
| LPARENtoken exp RPARENtoken
{ $$ = $2;}
%%
我的標記和類型的樣子:
%token BEGINtoken
%token COMMAtoken
%left DIVIDEtoken
%left TIMEStoken
%token ENDtoken
%token EOFtoken
%token EQtoken
%token <value> ICONSTtoken
%token <value> IDtoken
%token IStoken
%token LPARENtoken
%left PLUStoken MINUStoken
%token PRINTtoken
%token PROGRAMtoken
%token RPARENtoken
%token SEMItoken
%token VARtoken
%type <value> exp
%type <value> term
%type <value> factor