Lexical-Compiler/lex.cpp at main · deep-jain/Lexical-Compiler · GitHub

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#include <cctype>
#include <map>
#include "tokens.h"
using std::map;

static map<TokenType,string> tokenPrint = {
		{ IF, "IF" },
		{ SET, "SET" },
		{ PRINT, "PRINT" },
		{ LOOP, "LOOP" },
		{ BEGIN, "BEGIN" },
		{ END, "END" },

		{ ID, "ID" },

		{ ICONST, "ICONST" },
		{ SCONST, "SCONST" },

		{ PLUS, "PLUS" },
		{ MINUS, "MINUS" },
		{ STAR, "STAR" },
		{ SLASH, "SLASH" },
		{ LPAREN, "LPAREN" },
		{ RPAREN, "RPAREN" },

		{ SC, "SC" },
		{ NL, "NL" },

		{ ERR, "ERR" },

		{ DONE, "DONE" },
};


ostream& operator<<(ostream& out, const Token& tok) {
	TokenType tt = tok.GetTokenType();
	out << tokenPrint[ tt ];
	if( tt == ID || tt == ICONST || tt == SCONST || tt == ERR ) {
		out << "(" << tok.GetLexeme() << ")";
	}
	return out;
}

static map<string,TokenType> kwmap = {
		{ "if", IF },
		{ "set", SET },
		{ "print", PRINT },
		{ "loop", LOOP },
		{ "begin", BEGIN },
		{ "end", END },
};

Token
id_or_kw(const string& lexeme, int linenum) {
	TokenType tt = ID;

	auto kIt = kwmap.find(lexeme);
	if( kIt != kwmap.end() )
		tt = kIt->second;

	return Token(tt, lexeme, linenum);
}

Token
getNextToken(istream& in, int& linenum) {
	enum LexState { BEGIN, INID, INSTRING, ININT, INCOMMENT } lexstate = BEGIN;
	string lexeme;
	char ch;
    bool sawEscape;

	while(in.get(ch)) {

		switch( lexstate ) {
		case BEGIN:
            if( ch == '\n' ) {
                return Token(NL, "\n", linenum++);
            }

			if( isspace(ch) )
				continue;

			lexeme = ch;

			if( isalpha(ch) ) {
				lexstate = INID;
			}
			else if( ch == '"' ) {
				lexstate = INSTRING;
                sawEscape = false;
			}
			else if( isdigit(ch) ) {
				lexstate = ININT;
			}
			else if( ch == '#' ) {
				lexstate = INCOMMENT;
			}
			else {
				TokenType tt = ERR;
				switch( ch ) {
				case '+':
					tt = PLUS;
					break;
				case '-':
					tt = MINUS;
					break;
				case '*':
					tt = STAR;
					break;
				case '/':
					tt = SLASH;
					break;
				case '(':
					tt = LPAREN;
					break;
				case ')':
					tt = RPAREN;
					break;
				case ';':
					tt = SC;
					break;
				}
				return Token(tt, lexeme, linenum);
			}break;

		case INID:
			if( isalpha(ch) || isdigit(ch) ) {
				lexeme += ch;
			}
			else {
				in.putback(ch);
				return id_or_kw(lexeme, linenum);
			}break;

		case INSTRING:
            if( sawEscape ) {
                // last character was an escape, what's this one??
                sawEscape = false;
                if( ch == 'n' ) ch = '\n';
                // otherwise... it's unchanged
                lexeme += ch;
                break;
           }

            if( ch == '\\' ) {
                sawEscape = true;
                break;
            }

			lexeme += ch;
			if( ch == '\n' ) {
				return Token(ERR, lexeme, linenum);
			}
			if( ch == '"' ) {
				lexeme = lexeme.substr(1, lexeme.length()-2);
				return Token(SCONST, lexeme, linenum);
			}break;

		case ININT:
			if( isdigit(ch) ) {
				lexeme += ch;
			}
			else if( isalpha(ch) ) {
				lexeme += ch;
				return Token(ERR, lexeme, linenum);
			}
			else {
				in.putback(ch);
				return Token(ICONST, lexeme, linenum);
			} break;

		case INCOMMENT:
			if( ch == '\n' ) {
				in.putback(ch);
				lexstate = BEGIN;
			} break;
		}
	}

	if( in.eof() )
		return Token(DONE, "", linenum);
	return Token(ERR, "some strange I/O error", linenum);
}