【发布时间】：2019-02-04 02:07:41
【问题描述】：
我必须构建一个将 java 语言翻译成 pyhton 的编译器。我正在使用 Flex 和 Bison 工具。我创建了 flex 文件，并在 Bison 中为我必须实现的一些限制定义了句法语法（例如数组、循环管理、类管理、逻辑算术运算符的管理等）。 我无法理解如何处理语义规则。例如，我应该处理import语句和变量声明的语义，将变量添加到符号表中，然后处理翻译。 这是symboltable.h模块中符号表的结构：
struct symtable{
char *scopename; // key
struct symtable2 *subtable; // symble table secondary
UT_hash_handle hh; // to make the structure hash
}
struct symtable2 // secondary symbol structure
{
char *name; // Name of the symbol (key)
char *element; // it can be a variable or an array
char *type; // Indicates the type assumed by the token
(int, float, char, bool)
char *value; // value assigned to the variable
int dim; // Array size, it is zero in the case of a variable.
UT_hash_handle hh; // to make the structure hash
};
这是添加符号功能：
void add_symbol( char *name, char *current_scopename, char *element, char *current_type, char *current_value, int dim, int nr) { //Function to add a new symbol in the symbol table
struct symtable *s;
HASH_FIND_PTR(symbols, current_scopename, s);
if (s == NULL) {
s = (struct symtable *)malloc(sizeof *s);
s->scopename =current_scopename;
s->subtable=NULL;
s->scopename =current_scopename;
HASH_ADD_KEYPTR(hh,symbols,s->scopename,strlen(s->scopename),s);
}
struct symtable2 *s2;
HASH_FIND_PTR(symbols2, name, s2);
if (s2==NULL) {
s2 = (struct symtable2 *)malloc(sizeof *s2);
s2->name = name;
s2->element = element;
s2->type = current_type;
s2->value = current_value;
s2->dim = dim;
HASH_ADD_KEYPTR(hh,s->subtable,s2->name,strlen(s2->name),s2);
} else {
if (strcmp( s2->type,current_type) == 0){
s2->value =current_value;
} else {
printf("\033[01;31mRiga %i. [FATALE] SEMANTIC ERROR: assignment violates the primitive type of the variable.\033[00m\n", nr);
printf("\n\n\033[01;31mParsing failed.\033[00m\n");
}
}
}
这是bison文件的一部分，带有处理导入语句和变量声明的语法：
%{
#include <stdio.h>;
#include <ctype.h>;
#include <symboltable.h>;
file *f_ptr;
%}
%start program
%token NUMBER
%token ID
%token INT
%token FLOAT
%token DOUBLE
%token CHAR
%token IMPORT
%right ASSIGNOP
%left SCOR
%left SCAND
%left EQ NE
%left LT GT LE GE
%left ADD SUB
%left MULT DIV MOD
%right NOT
%left '(' ')' '[' ']'
%%
program
: ImportStatement GlobalVariableDeclarations
;
ImportStatement
: IMPORT LibraryName ';' { delete_file (); f_ptr = open_file (); fprintf(fptr, "import array \n"); }
;
LibraryName
: 'java.util.*'
;
GlobalVariableFieldDeclarations
: type GlobalVariableDeclarations ';'
;
GlobalVariableDeclarations
: GlobalVariableDeclaration
| GlobalVariableDeclarations ',' GlobalVariableDeclaration
;
GlobalVariableDeclaration
: VariableName
| VariableName ASSIGNOP VariableInitializer {if (typeChecking($1,$3)== 0) {$1= $3; $$=$1;}}
;
VariableName
: ID {$$ = $1 ;}
;
type
: INT
| CHAR
| FLOAT
| DOUBLE
| BOOLEAN
;
VariableInitializers
: VariableInitializer
| VariableInitializers ',' VariableInitializer
;
VariableInitializer
: ExpressionStatement
;
ExpressionStatement
: VariableName
| NUMBER
| ArithmeticExpression
| RelationalExpression
| BooleanExpression
;
ArithmeticExpression
: ExpressionStatement ADD ExpressionStatement
| ExpressionStatement SUB ExpressionStatement
| ExpressionStatement MULT ExpressionStatement
| ExpressionStatement DIV ExpressionStatement
| ExpressionStatement MOD ExpressionStatement
;
RelationalExpression
: ExpressionStatement GT ExpressionStatement
| ExpressionStatement LT ExpressionStatement
| ExpressionStatement GE ExpressionStatement
| ExpressionStatement LE ExpressionStatement
| ExpressionStatement EQ ExpressionStatement
| ExpressionStatement NE ExpressionStatement
;
BooleanExpression
: ExpressionStatement SCAND ExpressionStatement
| ExpressionStatement SCOR ExpressionStatement
| NOT ExpressionStatement
;
%%
int yyerror (char *s)
{
printf ("%s \n",s);
}
int main (void) {
return yyparse();
}
int typeChecking (variable1, variable2) {
struct symtable2 *s2;
s2=find_symbol (scopename, variable1);
if (s2!=NULL) {
int type1= s2->type;
char element1 = s2->element;
}
else{
printf("\n\n\033[01;31mVariable 1 not defined.\033[00m\n");
return -1;
}
s2=find_symbol (scopename, variable2);
if (s2!=NULL) {
int type2= s2->type;
char element2 = s2->element;
}
else{
printf("\n\n\033[01;31mVariable 2 not defined.\033[00m\n");
return -1;
}
if(element1=='variable' && element2=='variable'){
if (type1 == type2){
return 0;
}
else {
return 1;
}
}
else {
printf("\n\n\033[01;31m Different elements.\033[00m\n");
return -1;
}
}
我是野牛语法用于语义管理的初学者，在以下作品中我对相对语义规则有疑问：
GlobalVariableFieldDeclarations
: type GlobalVariableDeclarations ';'
;
GlobalVariableDeclarations
: GlobalVariableDeclaration
| GlobalVariableDeclarations ',' GlobalVariableDeclaration
;
GlobalVariableDeclaration
: VariableName
| VariableName ASSIGNOP VariableInitializer {if (typeChecking($1,$3)== 0) {$1= $3; $$=$1;}}
;
VariableName
: ID {$$ = $1 ;}
;
以这种方式管理 GlobalVariableDeclaration 产生式的语义是否正确？以及如何通过 add_symbol 函数在符号表中插入所需的参数值？ （或者更好的是，我如何从产生式开始获取所需的参数以将它们插入到我已经实现的 add_symbol 函数中？）请原谅我，但我是一个初学者，关于语义的很多事情我都不清楚。我希望你有耐心帮助我，我提前谢谢你。
【问题讨论】：
标签： parsing compiler-construction bison symbol-table semantic-analysis