Kevin Meredith kevinmeredith

https://www.linkedin.com/in/kevin-meredith-33422a11

kevinmeredith / Monoid.scala

Created October 24, 2013 02:27

Exercise from FP in Scala

	// EXERCISE 9: Implement a foldMap for IndexedSeq, a common supertype
	// for various data structures that provide efficient random access including Vector.
	// Your implementation should use the strategy of splitting the sequence in two,/
	// recursively processing each half, and then adding the answers together with the
	// monoid.
	def foldMapV[A,B](v: IndexedSeq[A], m: Monoid[B])(f: A => B): B = {
	def go(seq: List[B], acc: B): B = seq match {
	case x :: xs => go(xs, m.op(acc, x))
	case Nil => acc
	}

kevinmeredith / MonoidTest.scala

Created November 14, 2013 03:10

Example of composing Monoids from the book, "Functional Programming in Scala"

	object ComposingMonoids {

	// Beginning of monoid compoisition (from FP in Scala)
	// https://github.com/pchiusano/fpinscala/.../.../17.answer.scala
	def productMonoid[A, B](A: Monoid[A], B: Monoid[B]): Monoid[(A, B)] = {
	new Monoid[(A, B)] {
	def op(x: (A,B), y: (A,B) ) = (A.op(x._1, y._1) , B.op(x._2, y._2))
	val zero = (A.zero, B.zero)
	}
	}

kevinmeredith / Bag.scala

Created November 14, 2013 03:55

Creating a "bag" in Scala with foldLeft

	// Given a list of items, return a Map[A -> Int] where A is an element and Int is how many times it appears
	val result = List("a", "b", "a").foldLeft(Map[String, Int]())( (acc, el) =>
	if (acc.contains(el) ) {
	val x = acc.get(el).get
	acc + (el -> (x+1))
	}
	else { acc + (el -> 1) } )

	assert(result == Map("a" -> 2, "b" -> 1)

kevinmeredith / AssertEx.html

Last active January 1, 2016 11:09

"Secrets of the JavaScript Ninja" home-made assert

	<html>
	<head>
	<title>Test Suite</title>
	<script>
	(function() {
	var results;
	this.assert = function assert(value, desc) {
	var li = document.createElement("li");
	li.className = value ? "pass" : "fail";
	li.appendChild(document.createTextNode(desc));

kevinmeredith / MemoizeWClosure.js

Created December 27, 2013 16:52

Power of closures (from Secrets of the JavaScript Ninja)

	Function.prototype.memoized = function(key) {
	this._values = this._values \|\| {};
	return this._values[key] !== undefined ?
	this._values[key] :
	this._values[key] = this.apply(this, arguments);
	}

	Function.prototype.memoize = function() {
	var fn = this;
	return function() {

kevinmeredith / Applicative.scala

Last active January 2, 2016 08:29

Question wrt Applicative#apply from FP in Scala

	trait Applicative[F[_]] extends Functor[F] {

	def map2[A,B,C](fa: F[A], fb: F[B])(f: (A,B) => C): F[C]

	def apply[A,B](fab: F[A => B])(fa: F[A]): F[B] =
	map2(fa, fab)((x, f) => f(x))

	// [code elided]

	// Your comment says,

kevinmeredith / map3.scala

Created January 6, 2014 16:24

for comprehension trying to use map (rather than flatMap)

	object TestForComprehensionMap3 {

	def map3(a: Option[Int], b: Option[Int], c: Option[Int])(f: (Int, Int, Int) => Option[Int]): Option[Int] = {
	a.flatMap(x => b.flatMap(y => c.flatMap(z => f(x,y,z) ) ) )
	}

	def map3ForExpr(a: Option[Int], b: Option[Int], c: Option[Int])(f: (Int, Int, Int) => Option[Int]): Option[Int] = {
	for {
	x <- a
	y <- b

kevinmeredith / Test.scala

Last active January 3, 2016 15:49

REPL for this SO post - http://stackoverflow.com/questions/5328007/why-doesnt-option-have-a-fold-method

	scala> els
	res4: Int = 222

	scala> opt
	res5: Some[Int] = Some(1)

	scala> opt.foldLeft(els)((_,elem) => identity(elem))
	res9: Int = 1

	scala> val optNone: Option[Int] = None

kevinmeredith / PersonUtil.scala

Created February 11, 2014 16:01

PersonReads

	package common

	import play.api.libs.json._
	import play.api.libs.functional.syntax._

	object PersonUtil {
	implicit val PersonReads: Reads[Person] = (
	(JsPath \ "name").read[String] and
	(JsPath \ "age").read[Int]
	)((x,y) => new Person(x,y))

kevinmeredith / Test.scala

Last active August 29, 2015 13:56

Why does this work if Writes[Parent] should only be implicit?

	// Parent.java
	public class Parent {
	private String name;
	private Child child;

	public Parent(String name, Child child) {
	this.name = name;
	this.child = child;
	}