Question

我正在建立针对特定语言的兼容软件，我制作了lex扫描仪和yacc Parsar以及包含某些语言的文本文件，目标是构建适当的AST并进行打印，

我已经用我需要的所有规则制作了完整的yacc和lex文件，我使用代码运行它们：

yacc -d test.y
lex test.l
cc -o test y.tab.c -ll -Ly
./test < file.t

这些文件能够从文本文件创建解析器，而没有任何语法问题，因此使用lex和yacc进行扫描和解析即可。

我已经为AST的构建准备了功能，为了正确打印，我做了一个递归功能，可以按顺序扫描以打印所有树。

* i删除了大多数不相关的代码

一些yacc代码：

%{
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>

    typedef struct node {
        char* token;
        struct node *left;
        struct node *middle; 
        struct node *right;
    }node;



    node *mknode(char *token,node *left,node *middle,node *right);

    void printTree(node *tree);

    void yyerror(const char *s);

    int yylex();

    #define printTree

    #define YYSTYPE struct node*
    extern char *yytext;

%}
%start start
%token MULTI DIVISION BOOL CHAR INT REAL STRING INTPTR CHARPTR REALPTR IF ELSE WHILE FOR VAR FUNC PROC RETURN ASSIGN AND EQUAL GREATER GREATEREQUAL LESS LESSEQUAL MINUS NOT NOTEQUAL OR PLUS ADDRESS DEREFERENCE ABSUOLUT NULLL SEMICOLON COLUMS COMMA NEGATIVE_NUM LEFTBRACE RIGHTBRACE LEFTBRACKET RIGHTBRACKET COOMMENT PRESENT MAIN BOOLTRUE LEFTPAREN RIGHTPAREN BOOLFALSE INTEGER_CONST CHAR_CONST REAL_CONST ID STRING_CONST HEX_CONST 
%right ASSIGN ELSE DIVISION
%left LEFTBRACE RIGHTBRACE LEFTPAREN RIGHTPAREN
%left EQUAL GREATER GREATEREQUAL LESSEQUAL LESS NOTEQUAL
%left PLUS MINUS AND OR 
%left MULTI 

%%
    start: Main                {printTree($1);};

    Main: proc Main            {$$=mknode("CODE",$1,$2,NULL);}  
         |empty                {$$=mknode("CODE",$1,NULL,NULL);};


    id: ID                                               {$$=mknode(yytext,NULL,NULL,NULL);};


    leftParen: LEFTPAREN                                       {$$=mknode("(",NULL,NULL,NULL);};

    rightParen: RIGHTPAREN                                     {$$=mknode(")",NULL,NULL,NULL);};

    empty:                                               {$$=mknode("",NULL,NULL,NULL);};

    proc: PROC id leftParen paramsList rightParen Problock {$$=mknode("PROC",mknode($2->token,$3,$4,$5),NULL,$6);}
         |FUNC id leftParen paramsList rightParen returnInsideFuncDeclaration Problock {$$=mknode("FUNC",mknode($2->token,$3,$4,$5),$6,$7);};


    paramsList: startparamsList SEMICOLON paramsList     {$$=mknode("start_params",$1,mknode(";",NULL,NULL,NULL),$3);}
                |startparamsList                         {$$=mknode("start_params",$1,NULL,NULL);}
                |empty                                   {$$=mknode("start_params",$1,NULL,NULL);}; 

    startparamsList: id next_param_in_proc               {$$=mknode("start_params",$1,$2,NULL);};

    next_param_in_proc: COMMA id next_param_in_proc      {$$=mknode(",",$2,$3,NULL);}
                        |COLUMS varType                  {$$=mknode(":",$2,NULL,NULL);};



    Problock: leftBrace Procbody rightBrace              {$$=mknode("PROC",$1,$2,$3);};

    Procbody: BlockBody                                  {$$=mknode("BODY",$1,NULL,NULL);}
              |BlockBody return                          {$$=mknode("BODY",$1,$2,NULL);} ; 


    HelpToStatement: ProcStatement HelpToStatement       {$$=mknode("help to statment",$1,$2,NULL);}
                     |empty                              {$$=mknode("help to statment",$1,NULL,NULL);};

    HelpToTheProcedure: proc HelpToTheProcedure          {$$=mknode("help proc",$1,$2,NULL);}
                        |empty                           {$$=mknode("help proc",$1,NULL,NULL);};

    HelpDeclare: Declaration HelpDeclare                 {$$=mknode("declartion",$1,$2,NULL);}
                 |empty                                  {$$=mknode("declartion",$1,NULL,NULL);};

    BlockBody: HelpToTheProcedure HelpDeclare HelpToStatement   {$$=mknode("Body",$1,$2,$3);};   


    ProcStatement:   exp SEMICOLON 
                     |structOfCond
                     |block;

%%
#include "lex.yy.c"

int main()
{
    return yyparse();
}

node *mknode(char *token, node *left, node *middle, node *right)
{
    node *newnode = (node*)malloc(sizeof(node));
    char *newstr = (char*)malloc(sizeof(token)+1);
    strcpy(newstr,token);
    newnode->left = left;
    newnode->middle = middle;
    newnode->right = right;
    newnode->token = newstr;
    return newnode;
}
void printtree(node *tree)
{
    printf("%s\n",tree->token);
    if(tree->left)
        printtree(tree->left);
    if(tree->middle)
        printtree(tree->middle);
    if(tree->right)
        printtree(tree->right);
}

void yyerror(const char *str)
{
    printf("%s - %s in line:%d \n",str,yytext,counter);
}

所以我设法从该语言构建AST，但不打印它，出于某种原因，函数'printTree'什么也没做，

如果我尝试这样打印：printf("%s", $1->token)或printf("%s", $1->left->token)，那么一切都很好，每个令牌都在其应有的位置，那么为什么我不能使用递归函数打印它们？

Answer 1

您正在使用printTree将#define printTree定义为空。因此，printTree($1);被宏扩展为($1);，这是无操作的。另一方面，永远不会调用您的函数printtree（不使用大写字母）。

因此，您应该删除#define，向前声明printtree函数，然后在操作中调用它。

如何在yacc中使用递归来打印AST？

1 个答案: