parse.h

<compiler construction principles and practice>书中定义的tiny语言编译器。

class Parse:public Scan, public TreeNode
{
private:
   
	TokenType token;
	TreeNode * stmt_sequence(void);
	TreeNode * statement(void);
	TreeNode * if_stmt(void);
	TreeNode * repeat_stmt(void);
	TreeNode * assign_stmt(void);
	TreeNode * read_stmt(void);
	TreeNode * write_stmt(void);
	TreeNode * exp(void);
	TreeNode * simple_exp(void);
	TreeNode * term(void);
	TreeNode * factor(void);
	void SyntaxError(char * message);
	void match(TokenType expected);


public:
	Parse(char *);
	TreeNode * parse();
};

Parse::Parse(char* name):Scan(name){};

void Parse::SyntaxError(char * message)
{ 
	cout<<"\nSyntax error at line "<<lineno<<"  "<<message<<endl;
	
    Error = 1;
}

void Parse::match(TokenType expected)
{ 
	if (token == expected) token = getToken();
	else 
	{
		SyntaxError("unexpected token -> ");
		printToken(token,tokenString);
		cout<<"   ";
	}
}

TreeNode * Parse::stmt_sequence(void)
{ 
	TreeNode * t = statement();
    TreeNode * p = t;
    while ((token!=ENDFILE) && (token!=END) && (token!=ELSE) && (token!=UNTIL))
    {
	   TreeNode * q;
       match(SEMI);
       q = statement();
       if (q!=NULL) 
	   {
			if (t==NULL) t = p = q;
			else 
			{
				 p->sibling = q;
				p = q;
			}
		}
	}
	return t;
}

TreeNode * Parse::statement(void)
{
	TreeNode * t = NULL;
    switch (token) 
	{
		case IF :		 t = if_stmt();		 break;
		case REPEAT :	 t = repeat_stmt();  break;
		case ID :		 t = assign_stmt();  break;
		case READ :		 t = read_stmt();    break;
		case WRITE :	 t = write_stmt();   break;
		default :
			SyntaxError("unexpected token -> ");
            printToken(token,tokenString);
            token = getToken();
            break;
	} 
    return t;
}

TreeNode * Parse::if_stmt(void)
{ 
	TreeNode * t = NewStmtNode(IfK);
    match(IF);
    if (t!=NULL) t->child[0] = exp();
    match(THEN);
    if (t!=NULL) t->child[1] = stmt_sequence();
    if (token==ELSE)
	{
	    match(ELSE);
		if (t!=NULL) t->child[2] = stmt_sequence();
	}
	match(END);
	return t;
}


TreeNode * Parse::repeat_stmt(void)
{ 
	TreeNode * t = NewStmtNode(RepeatK);
    match(REPEAT);
    if (t!=NULL) t->child[0] = stmt_sequence();
    match(UNTIL);
    if (t!=NULL) t->child[1] = exp();
    return t;
}

TreeNode * Parse::assign_stmt(void)
{
	TreeNode * t = NewStmtNode(AssignK);
	if((t != NULL) && (token == ID) )
		t->attr.name = CopyString(tokenString);
	match(ID);
	match(ASSIGN);
	if(t != NULL)
		t->child[0] = exp();
	return t;
}

TreeNode * Parse::read_stmt(void)
{ 
	TreeNode * t = NewStmtNode(ReadK);
    match(READ);
    if ((t!=NULL) && (token==ID))
		t->attr.name = CopyString(tokenString);
    match(ID);
    return t;
}

TreeNode * Parse::write_stmt(void)
{ 
	TreeNode * t = NewStmtNode(WriteK);
    match(WRITE);
    if (t!=NULL) t->child[0] = exp();
    return t;
}

TreeNode* Parse::exp(void)
{ 
	TreeNode * t = simple_exp();
    if ((token==LT)||(token==EQ)) 
	{
		TreeNode * p = NewExpNode(OpK);
		if (p!=NULL)
		{
		    p->child[0] = t;
			p->attr.op = token;
			t = p;
		}
		match(token);
		if (t!=NULL)
			t->child[1] = simple_exp();
	}
	return t;
}

TreeNode * Parse::simple_exp(void)
{ 
	TreeNode * t = term();
	while ((token==PLUS)||(token==MINUS))
	{
		TreeNode * p = NewExpNode(OpK);
		if (p!=NULL)
		{
			p->child[0] = t;
			p->attr.op = token;
			t = p;
			match(token);
			t->child[1] = term();
		}
	}
	return t;
}

TreeNode * Parse::term(void)
{
	TreeNode * t = factor();
	while ((token==TIMES)||(token==OVER))
    {
		TreeNode * p = NewExpNode(OpK);
		if (p!=NULL)
		{
			p->child[0] = t;
			p->attr.op = token;
			t = p;
			match(token);
			p->child[1] = factor();
		}
	}
	return t;
}

TreeNode * Parse::factor(void)
{
	TreeNode * t = NULL;
	switch (token)
	{
	    case NUM :
			t = NewExpNode(ConstK);
			if ((t!=NULL) && (token==NUM))
				t->attr.val = atoi(tokenString);
			match(NUM);
			break;
		case ID :
			t = NewExpNode(IdK);
			if ((t!=NULL) && (token==ID))
				t->attr.name = CopyString(tokenString);
			match(ID);
			break;
		case LPAREN :
			match(LPAREN);
		    t = exp();
		    match(RPAREN);
		    break;
		default:
			SyntaxError("unexpected token -> ");
			printToken(token,tokenString);
		    token = getToken();
			break;
    }
	return t;
}


TreeNode * Parse::parse(void)
{ 
	TreeNode * t;

	token = getToken();
	
	t = stmt_sequence();
	
	printTree(t);
	if (token!=ENDFILE)
		SyntaxError("Code ends before file\n");
	cout<<"\n\n";
	return t;
}