Simple compiler

gistfile1.js

/**
 * A simple arithmetic language that consists of the following keywords
 * 
 * reset
 * 		reset x, creates a variable x if it doesnot exist and assigns 0 as its value 
 * increment
 * 		increment x, increments a previously declared variable x, generates compiler warning if it doesnot have x already.
 * loop
 *		loop x, loops the following statements until endloop x times, generates a compiler warning if x is not defined already.
 * endloop
 * 		limits the statements within a loop.
 *
 * Every line should have exactly one statement and should begin with a keyword followed by a variable except endloop
 * A variable should begin with an alphabet.
 * Arguments to the program should be positive numeric values only.
 * 
 * Example program to increment x a given number of times
 * reset x
 * loop a
 * increment x
 * endloop
 * 
 */

var Compiler = function() {
	this.resetKeyword = new KeywordSymbol("reset", true);
	this.incrementKeyword = new KeywordSymbol("increment", true);
	this.loopKeyword = new KeywordSymbol("loop", true);
	this.endLoopKeyword = new KeywordSymbol("endloop", false);
	this.loopKeyword.shouldBeFollowedBySymbol(this.endLoopKeyword);
	this.endLoopKeyword.shouldBePreceededBySymbol(this.loopKeyword);
	this.parser = new Parser([this.resetKeyword, this.incrementKeyword, this.loopKeyword, this.endLoopKeyword]);

	return this;
}

Compiler.prototype.compile = function(text) {
	return this.parser.parse(text);
}

Compiler.prototype.constructRuntime = function(statements) {

	var jsString = "";

	for (var i = 0; i < statements.length; i++) {
		var statement = statements[i];
		if (statement.keywordSymbol == this.resetKeyword) {
			jsString += "\n" + statement.variable + "= reset();";
		} else if (statement.keywordSymbol == this.incrementKeyword) {
			jsString += "\n" + statement.variable + "= increment(" + statement.variable + ")";
		} else if (statement.keywordSymbol == this.loopKeyword) {
			jsString += "\nloop(" + statement.variable + ", function() { \n";
		} else if (statement.keywordSymbol == this.endLoopKeyword) {
			jsString += "\n});"
		}
	}
	return jsString;
}

/**
 * public method, 
 * @param, text, sourceCode to execute
 */
Compiler.prototype.execute = function(text, arguments) {
	try {
	var statements = this.compile(text);

	var variables = this.extractVariables(statements);

	var evalString = "var fun = function() {\n";
	evalString += this.prependVariables(variables, arguments);

	evalString += this.constructRuntime(statements);

	evalString += this.appendReturnVariables(variables);

	evalString += "}";

	console.log(evalString);

	eval(evalString);

	result = fun();
	return result;
	} catch (err) {
		alert(err.description);
	}
}

Compiler.prototype.extractVariables = function(statements) {
	var varSet = [];
	for (var i = 0; i < statements.length; i++) {
		if (!statements[i].keywordSymbol.acceptsVariable) {
			continue;
		}
		var variable = statements[i].variable;
		if (varSet.indexOf(variable) != -1) {
			continue;
		}
		varSet[varSet.length] = variable;
	};
	return varSet;
}

/**
 * arguments will be indexed from 0 to n-1 and predefined variables will be from 
 */
Compiler.prototype.prependVariables = function(variables, arguments) {
	var jsString = "";
	for (var i = 0; i < variables.length; i++) {
		var variable = variables[i];
		if (arguments.hasOwnProperty(variable)) {
			jsString += "var " + variable + " = " + arguments[variable] + ";";
		} else {
			jsString += "var " + variable + " = 0;";
		}
	}
	return jsString;
}

Compiler.prototype.appendReturnVariables = function(variables) {
	var jsString = "\nreturn {";
	for (var i = 0; i < variables.length; i++) {
		var variable = variables[i];
		jsString += "'" + variable + "' : " + variable + ","
	};
	jsString += "}";
	return jsString;
}

//--end Compiler-------------------------------//



//--begin Parser-------------------------------//
var Parser = function(keywordSymbols) {
	this.keywordSymbols = keywordSymbols;
	return this;
}

Parser.prototype.parse = function(str) {
	var lines = this.getLines(str);

	var compiledStatements = [];

	var statementStackWaitingForMatches = [];

	for (i = 0; i< lines.length; i++) {
		var tokens = this.getWords(lines[i]);
		if (tokens.length > 2) {
			throw new ParseException(i+1, 3, "Unrecognized symbol", "Symbol "+tokens[2]+" not expected");
		}
		if (!this.isValidKeyword(tokens[0])) {
			throw new ParseException(i+1, 1, "Invalid keyword", "Every statement should begin with a keyword");
		}

		var keywordSymbol = this.getKeywordSymbol(tokens[0]);
		if (keywordSymbol.acceptsVariable) {
			if (!this.isValidVariable(tokens[1])) {
				throw new ParseException(i+1, 2, "Invalid variable", "Cannot be a valid variable "+tokens[1]);
			}
		} else {
			if (tokens.length > 1) {
				throw new ParseException(i + 1, 2, "Unrecognized symbol", "Symbol "+tokens[1]+" not expected after "+keywordSymbol.name);
			}
		}

		var statement = new Statement(keywordSymbol, tokens[1]);
		compiledStatements[compiledStatements.length] = statement;


		if (keywordSymbol.symbolToFollow != null) {
			statementStackWaitingForMatches[statementStackWaitingForMatches.length] = statement;
		}

		if (keywordSymbol.symbolToPreceed != null) {
			if (statementStackWaitingForMatches.length == 0) {
				throw new ParseException( i + 1 , 1, "Unmatched statement", "This statement should be preceeded by a "+keywordSymbol.name+" statement");
			}

			if (statementStackWaitingForMatches[statementStackWaitingForMatches.length-1].keywordSymbol.name == statement.keywordSymbol.symbolToPreceed.name) {
				statementStackWaitingForMatches.pop();
			}
		}
	}

	if (statementStackWaitingForMatches.length > 0) {
		throw new ParseException(lines.length , 1, "Open loop", "loop not closed for "+statementStackWaitingForMatches[0].keywordSymbol.name+" "+statementStackWaitingForMatches[0].variable);
	}
	return compiledStatements;
}

Parser.prototype.isValidKeyword = function(token) {
	return this.getKeywordSymbol(token) != null;
}

/**
 * Makes sure the given token matches one of the keywordSymbols
 * return true, if is one of a given keywords.
 */
Parser.prototype.getKeywordSymbol = function(token) {
	for (var i = 0; i < this.keywordSymbols.length; i++) {
		if (this.keywordSymbols[i].name === token) {
			return this.keywordSymbols[i];
		}
	};
	return null;
}

Parser.prototype.isValidVariable = function(token) {
	if (this.isValidKeyword(token)) {
		return false;
	}

	if (this.isSpecialVariable(token)) {
		return true;
	}

	if (/^[a-zA-Z0-9]*$/.test(token)) {
		return true;
	}

	return false;
}

//special kind of variable that starts with _ like _1, _2 etc
Parser.prototype.isSpecialVariable = function(token) {
	// if (/^[_][0-9]*/.test(token)) {
	// 	return true;
	// }	
	return false;
}

/**
 * Simply returns string tokens separated by new line character
 */
Parser.prototype.getLines = function(text) {
	return text.match(/[^\r\n]+/g);
}

/**
 * return, array of tokens separated by a white space character.
 */
Parser.prototype.getWords = function(text) {
	return text.match(/\S+/g);
}

//---end of Parser------------------------------//



//----begin KeyworkSymbol----------------------------//
var KeywordSymbol = function(name, acceptsVariable) {
	this.name = name;
	this.acceptsVariable = acceptsVariable;
	this.symbolToFollow = null;
	this.symbolToPreceed = null;
	return this;
}

KeywordSymbol.prototype.shouldBeFollowedBySymbol = function(keywordSymbol) {
	this.symbolToFollow = keywordSymbol;
}

KeywordSymbol.prototype.shouldBePreceededBySymbol = function(keywordSymbol) {
	this.symbolToPreceed = keywordSymbol;
}
//-----end Keyword Symbol----------------------------//

//---------------------------------//
var ParseException = function(lineNo, symbolNo, type, description) {
	this.lineNo = lineNo;
	this.symbolNo = symbolNo;
	this.type = type;
	this.description = description;
	return this;
}
//---------------------------------//

//---------------------------------//
var Statement = function(keywordSymbol, variable) {
	this.keywordSymbol = keywordSymbol;
	this.variable = variable;
	return this;
}
//---------------------------------//

//-----------Runtime---------------//

function increment(x) {
    return x+1;
}

function loop(x, callback) {
    var i;
    for(i=0; i< x; i++) {
        callback();
    }
}

function reset() {
    return 0;
}

//-----------end Runtime---------------//

http://jsfiddle.net/nv631L97/1/

a - 1

---

x=0
y = 0

for a

x = y

y++

end for

a - b

---

x = 0

for b

z=0
y = 0

for a

z = y

y++

end for

x = z

end for