parse.cpp

/* Incomplete Implementation of Recursive-Descent Parser
 * parse.cpp
 * Programming Assignment 2
 * Fall 2021
*/

#include "parse.h"

map<string, bool> defVar;
map<string, Token> SymTable;

namespace Parser {
	bool pushed_back = false;
	LexItem	pushed_token;

	static LexItem GetNextToken(istream& in, int& line) {
		if( pushed_back ) {
			pushed_back = false;
			return pushed_token;
		}
		return getNextToken(in, line);
	}

	static void PushBackToken(LexItem & t) {
		if( pushed_back ) {
			abort();
		}
		pushed_back = true;
		pushed_token = t;	
	}

}

static int error_count = 0;

int ErrCount()
{
    return error_count;
}

void ParseError(int line, string msg)
{
	++error_count;
	cout << line << ": " << msg << endl;
}


//Decl = Type IdentList 
//Type = INTEGER | REAL | CHAR
bool DeclStmt(istream& in, int& line) {
	bool status = false;
	LexItem tok;
	//cout << "in Decl" << endl;
	LexItem t = Parser::GetNextToken(in, line);
	
	if(t == INT || t == FLOAT ) {
		status = IdentList(in, line, t);
		//cout<< "returning from IdentList" << " " << (status? 1: 0) << endl;
		if (!status)
		{
			ParseError(line, "Incorrect variable in Declaration Statement.");
			return status;
		}
		}
	else{
		Parser::PushBackToken(t);
		ParseError(line, "Incorrect Type.");
		return false;
	}
	return true;
}

bool Stmt(istream& in, int& line){
	bool status=true;
	//cout << "in Stmt" << endl;
	LexItem t = Parser::GetNextToken(in, line);
	
	switch( t.GetToken() ) {
	case INT: case FLOAT: 
		Parser::PushBackToken(t);
		status = DeclStmt(in, line);
		if(!status)
		{
			ParseError(line, "Incorrect Declaration Statement.");
			return status;
		}
		break;
	case IF: case WRITE: case IDENT: 
		Parser::PushBackToken(t);
		status = ControlStmt(in, line);
		if(!status)
		{
			ParseError(line, "Incorrect control Statement.");
			return status;
		}
		break;
	default:
		Parser::PushBackToken(t);
	}
	return status;
}

//WriteStmt:= wi, ExpreList 
bool WriteStmt(istream& in, int& line) {
	LexItem t;
	//cout << "in WriteStmt" << endl;
		
	bool ex = ExprList(in, line);
	
	if( !ex ) {
		ParseError(line, "Missing expression after Write");
		return false;
	}
	
	//Evaluate: print out the list of expressions values

	return ex;
}