dojo.provide("dojox.lang.functional.lambda");

// This module adds high-level functions and related constructs:
//	- anonymous functions built from the string

// Acknoledgements:
//	- lambda() is based on work by Oliver Steele 
//		(http://osteele.com/sources/javascript/functional/functional.js)
//		which was published under MIT License

// Notes:
//	- lambda() produces functions, which after the compilation step are 
//		as fast as regular JS functions (at least theoretically).

// Lambda input values:
//	- returns functions unchanged
//	- converts strings to functions
//	- converts arrays to a functional composition

(function(){
	var df = dojox.lang.functional, lcache = {};

	// split() is augmented on IE6 to ensure the uniform behavior
	var split = "ab".split(/a*/).length > 1 ? String.prototype.split :
			function(sep){
				 var r = this.split.call(this, sep),
					 m = sep.exec(this);
				 if(m && m.index == 0){ r.unshift(""); }
				 return r;
			};
			
	var lambda = function(/*String*/ s){
		var args = [], sects = split.call(s, /\s*->\s*/m);
		if(sects.length > 1){
			while(sects.length){
				s = sects.pop();
				args = sects.pop().split(/\s*,\s*|\s+/m);
				if(sects.length){ sects.push("(function(" + args + "){return (" + s + ")})"); }
			}
		}else if(s.match(/\b_\b/)){
			args = ["_"];
		}else{
			var l = s.match(/^\s*(?:[+*\/%&|\^\.=<>]|!=)/m),
				r = s.match(/[+\-*\/%&|\^\.=<>!]\s*$/m);
			if(l || r){
				if(l){
					args.push("$1");
					s = "$1" + s;
				}
				if(r){
					args.push("$2");
					s = s + "$2";
				}
			}else{
				// the point of the long regex below is to exclude all well-known 
				// lower-case words from the list of potential arguments
				var vars = s.
					replace(/(?:\b[A-Z]|\.[a-zA-Z_$])[a-zA-Z_$\d]*|[a-zA-Z_$][a-zA-Z_$\d]*:|this|true|false|null|undefined|typeof|instanceof|in|delete|new|void|arguments|decodeURI|decodeURIComponent|encodeURI|encodeURIComponent|escape|eval|isFinite|isNaN|parseFloat|parseInt|unescape|dojo|dijit|dojox|window|document|'(?:[^'\\]|\\.)*'|"(?:[^"\\]|\\.)*"/g, "").
					match(/([a-z_$][a-z_$\d]*)/gi) || [], t = {};
				dojo.forEach(vars, function(v){
					if(!(v in t)){
						args.push(v);
						t[v] = 1;
					}
				});
			}
		}
		return {args: args, body: s};	// Object
	};

	var compose = function(/*Array*/ a){
		return a.length ? 
					function(){
						var i = a.length - 1, x = df.lambda(a[i]).apply(this, arguments);
						for(--i; i >= 0; --i){ x = df.lambda(a[i]).call(this, x); }
						return x;
					}
				: 
					// identity
					function(x){ return x; };
	};

	dojo.mixin(df, {
		// lambda
		rawLambda: function(/*String*/ s){
			// summary:
			//		builds a function from a snippet, or array (composing),
			//		returns an object describing the function; functions are
			//		passed through unmodified.
			// description:
			//		This method is to normalize a functional representation (a
			//		text snippet) to an object that contains an array of
			//		arguments, and a body , which is used to calculate the
			//		returning value.
			return lambda(s);	// Object
		},
		buildLambda: function(/*String*/ s){
			// summary:
			//		builds a function from a snippet, returns a string, which
			//		represents the function.
			// description:
			//		This method returns a textual representation of a function
			//		built from the snippet. It is meant to be evaled in the
			//		proper context, so local variables can be pulled from the
			//		environment.
			s = lambda(s);
			return "function(" + s.args.join(",") + "){return (" + s.body + ");}";	// String
		},
		lambda: function(/*Function|String|Array*/ s){
			// summary:
			//		builds a function from a snippet, or array (composing),
			//		returns a function object; functions are passed through
			//		unmodified.
			// description:
			//		This method is used to normalize a functional
			//		representation (a text snippet, an array, or a function) to
			//		a function object.
			if(typeof s == "function"){ return s; }
			if(s instanceof Array){ return compose(s); }
			if(s in lcache){ return lcache[s]; }
			s = lambda(s);
			return lcache[s] = new Function(s.args, "return (" + s.body + ");");	// Function
		},
		clearLambdaCache: function(){
			// summary:
			//		clears internal cache of lambdas
			lcache = {};
		}
	});
})();
