step3.js

step3.js

function add1(v) { return v + 1; }
function isOdd(v) { return v % 2 == 1; }
function sum(total,v) { return total + v; }

function listReduction(list,v) {
	list.push(v);
	return list;
}

function mapReducer(fn) {
	return function(reductionFn){
		return function(list,v){
			return reductionFn( list, fn(v) );
		};
	};
}

function filterReducer(fn) {
	return function(reductionFn){
		return function(list,v){
			if (fn(v)) return reductionFn( list, v );
			return list;
		};
	};
}

// no longer used
function listSumReduction(list,v) {
	list[0] = sum(list[0] || 0,v);
	return list;
}

function identity(v) { return v; }

// no longer used, but this is f-ing rad!
function reduceReducer(reductionFn){
	return mapReducer(identity)(reductionFn);
}


var list = [2,5,8,11,14,17,20];

list
.reduce( mapReducer(add1)(listReduction), [] )
.reduce( filterReducer(isOdd)(listReduction), [] )
.reduce( sum, 0 ) // sum is a reduce, must start with 0
//48

step4.js

function add1(v) { return v + 1; }
function isOdd(v) { return v % 2 == 1; }
function sum(total,v) { return total + v; }

function composeRight(fn1,fn2) {
	return function(...args){
		return fn1(fn2(...args));	
	};
}

function listReduction(list,v) {
	list.push(v);
	return list;
}

function mapReducer(fn) {
	return function(reductionFn){
		return function(list,v){
			return reductionFn( list, fn(v) );
		};
	};
}

function filterReducer(fn) {
	return function(reductionFn){
		return function(list,v){
			if (fn(v)) return reductionFn( list, v );
			return list;
		};
	};
}

function listSumReduction(list,v) {
	list[0] = sum(list[0] || 0,v);
	return list;
}

function identity(v) { return v; }

function reduceReducer(reductionFn){
	return mapReducer(identity)(reductionFn);
}


var list = [2,5,8,11,14,17,20];

var transducer = 
	composeRight(
		mapReducer(add1),
		filterReducer(isOdd)
	)(sum)

list
.reduce( transducer, 0 );
// 48