void program() {
	token tok =  next_token();
	switch(tok){
		case 'begin':
		match('begin'); code(); match('end');
	}

void code() {
	token tok = next_token();
	switch(tok){
		case 'end':
		case 'endif':
		case 'else':
		case 'endwhile': return;
		case 'if': instlist();
		case 'while': instlist();
		case 'VARNAME': instlist();
		case 'for': instlist();
		case 'print': instlist();
		case 'read': instlist();
		default :
		syntax_error ( tok ) ; break ;
	}
}

void instlist() {
	token tok = next_token();
	switch(tok){
		case 'VARNAME':
		case 'IF':
		case 'WHILE':
		case 'FOR':
		case 'PRINT':
		case 'READ': instruction(); instlisttail();
		default : syntax_error ( tok ) ; break ;
	}
}

void instlisttail() {
	token tok = next_token();
	switch(tok) {
		case 'END':
		case 'ENDIF':
		case 'ELSE': return;
		case 'SEMICOLON': match('SEMICOLON'); instlist();
		default : syntax_error ( tok ) ; break ;
	}
}

void instruction() {
	token tok = next_token();
	switch(tok) {
		case 'VARNAME': assign();
		case 'IF': _if();
		case 'WHILE': _while();
		case 'FOR': _for();
		case 'PRINT': _print();
		case 'READ': _read();
		default : syntax_error ( tok ) ; break ;
	}
}