define(["dojo/_base/lang", "dojo/_base/array", "dojo/_base/kernel", "./lambda"],
	function(lang, arr, kernel, df){

// This module adds high-level functions and related constructs:
//	- "fold" family of functions

// Notes:
//	- missing high-level functions are provided with the compatible API:
//		foldl, foldl1, foldr, foldr1
//	- missing JS standard functions are provided with the compatible API:
//		reduce, reduceRight
//	- the fold's counterpart: unfold

// Defined methods:
//	- take any valid lambda argument as the functional argument
//	- operate on dense arrays
//	- take a string as the array argument
//	- take an iterator objects as the array argument (only foldl, foldl1, and reduce)

	var empty = {};

	lang.mixin(df, {
		// classic reduce-class functions
		foldl: function(/*Array|String|Object*/ a, /*Function*/ f, /*Object*/ z, /*Object?*/ o){
			// summary:
			//		repeatedly applies a binary function to an array from left
			//		to right using a seed value as a starting point; returns the final
			//		value.
			if(typeof a == "string"){ a = a.split(""); }
			o = o || kernel.global; f = df.lambda(f);
			var i, n;
			if(lang.isArray(a)){
				// array
				for(i = 0, n = a.length; i < n; z = f.call(o, z, a[i], i, a), ++i);
			}else if(typeof a.hasNext == "function" && typeof a.next == "function"){
				// iterator
				for(i = 0; a.hasNext(); z = f.call(o, z, a.next(), i++, a));
			}else{
				// object/dictionary
				for(i in a){
					if(!(i in empty)){
						z = f.call(o, z, a[i], i, a);
					}
				}
			}
			return z;	// Object
		},
		foldl1: function(/*Array|String|Object*/ a, /*Function|String|Array*/ f, /*Object?*/ o){
			// summary:
			//		repeatedly applies a binary function to an array from left
			//		to right; returns the final value.
			if(typeof a == "string"){ a = a.split(""); }
			o = o || kernel.global; f = df.lambda(f);
			var z, i, n;
			if(lang.isArray(a)){
				// array
				z = a[0];
				for(i = 1, n = a.length; i < n; z = f.call(o, z, a[i], i, a), ++i);
			}else if(typeof a.hasNext == "function" && typeof a.next == "function"){
				// iterator
				if(a.hasNext()){
					z = a.next();
					for(i = 1; a.hasNext(); z = f.call(o, z, a.next(), i++, a));
				}
			}else{
				// object/dictionary
				var first = true;
				for(i in a){
					if(!(i in empty)){
						if(first){
							z = a[i];
							first = false;
						}else{
							z = f.call(o, z, a[i], i, a);
						}
					}
				}
			}
			return z;	// Object
		},
		foldr: function(/*Array|String*/ a, /*Function|String|Array*/ f, /*Object*/ z, /*Object?*/ o){
			// summary:
			//		repeatedly applies a binary function to an array from right
			//		to left using a seed value as a starting point; returns the final
			//		value.
			if(typeof a == "string"){ a = a.split(""); }
			o = o || kernel.global; f = df.lambda(f);
			for(var i = a.length; i > 0; --i, z = f.call(o, z, a[i], i, a));
			return z;	// Object
		},
		foldr1: function(/*Array|String*/ a, /*Function|String|Array*/ f, /*Object?*/ o){
			// summary:
			//		repeatedly applies a binary function to an array from right
			//		to left; returns the final value.
			if(typeof a == "string"){ a = a.split(""); }
			o = o || kernel.global; f = df.lambda(f);
			var n = a.length, z = a[n - 1], i = n - 1;
			for(; i > 0; --i, z = f.call(o, z, a[i], i, a));
			return z;	// Object
		},
		// JS 1.8 standard array functions, which can take a lambda as a parameter.
		reduce: function(/*Array|String|Object*/ a, /*Function|String|Array*/ f, /*Object?*/ z){
			// summary:
			//		apply a function simultaneously against two values of the array
			//		(from left-to-right) as to reduce it to a single value.
			return arguments.length < 3 ? df.foldl1(a, f) : df.foldl(a, f, z);	// Object
		},
		reduceRight: function(/*Array|String*/ a, /*Function|String|Array*/ f, /*Object?*/ z){
			// summary:
			//		apply a function simultaneously against two values of the array
			//		(from right-to-left) as to reduce it to a single value.
			return arguments.length < 3 ? df.foldr1(a, f) : df.foldr(a, f, z);	// Object
		},
		// the fold's counterpart: unfold
		unfold: function(/*Function|String|Array*/ pr, /*Function|String|Array*/ f,
						/*Function|String|Array*/ g, /*Object*/ z, /*Object?*/ o){
			// summary:
			//		builds an array by unfolding a value
			o = o || kernel.global; f = df.lambda(f); g = df.lambda(g); pr = df.lambda(pr);
			var t = [];
			for(; !pr.call(o, z); t.push(f.call(o, z)), z = g.call(o, z));
			return t;	// Array
		}
	});
});
