function Position() {
	this.advance = function(n) {
		this.absolute += n;
		this.col += n;
	}

	this.newline = function() {
		this.col = 0;
		this.line++;
	}

	this.copy_from = function(that) {
		this.absolute = that.absolute;
		this.col = that.col;
		this.line = that.line;
	}

	this.reset = function() {
		this.absolute = 0;
		this.line = 1;
		this.col = 0;
	}

	this.reset();
}

function Token(type, text) {
	this.type = type;
	this.text = text;
	this.toString = function() {
		return "(" + this.type + ", \"" + this.text + "\")";
	}
}

function match_token(string) {
	var i, m;
	for (i=1; i<arguments.length; i++) {
		if (m = string.match(arguments[i][1])) {
			return new Token(arguments[i][0], m[0]);
		}
	}
	return null;
}

function Stream(text) {
	this.text = text;
	this.length = text.length;
	this.pos = new Position();
	this.lastpos = new Position();

	this.next = function() {
		while (1) {
			this.lastpos.copy_from(this.pos);

			if (this.pos.absolute >= this.length)
				return new Token("EOF", "EOF");
	
			var match = match_token(this.text.substring(this.pos.absolute),
				["COMMENT"   , /^WTF[^\n]*/             ],
				["SPACE"     , /^[ \t]+/                ],
				["IDENTIFIER", /^[A-Za-z_][A-Za-z0-9_]*/],
				["NUMBER"    , /^[0-9]+/                ],
				["ARROW"     , /^(\<-|-\>)/             ],
				["OP"        , /^[~\\:@]/               ],
				["NEWLINE"   , /^\n/                    ],
				["BRACKET"   , /^[\[\]]/                ],
				["UNKNOWN"   , /^./                     ]);
	
			if (match) {
				this.pos.advance(match.text.length);
				if (match.type == "NEWLINE")
					this.pos.newline();
				else if (match.type == "UNKNOWN")
					this.error("Token '" + match.text + "' never heard of");
				else if (match.type!="SPACE" && match.type!="COMMENT")
					return match;
			}
			else {
				throw "Ouch!";
			}
		}
	}

	this.back = function() {
		this.pos.copy_from(this.lastpos);
	}

	this.enlist = function() {
		var ls = [];
		var m;
		while (m=this.next(), m.type!="EOF")
			ls.push(m.text);
		return ls;
	}

	this.error = function(msg) {
		throw "Error at line " + this.lastpos.line + ", column " + this.lastpos.col + ": " + msg;
	}

	this.reset = function() {
		this.lastpos.copy_from(pos);
		this.pos.reset();
	}
}