var shader = (function(){
	var fn_str, fn, lex
	var exports = {}
	
	exports.init = function(){
		lex = new Lex (0, 0)
		exports.build(demo_shader.innerHTML)
	}
	exports.build = function (fn_str){
		new_fn = new Function('lex', 'x', 'y', fn_str)
		try {
			new_fn(lex, 0, 0)
		}
		catch (e) {
			throw 'Shader execution error'
		}
		exports.fn = fn = new_fn
		return fn
	}
	exports.run = function(canvas){
		canvas.forEach(function(lex, y, x){
			fn(lex, x, y)
			lex.build()
		})
	}
	
	return exports

})()