Tom Wey tjmw

Elm Building Blocks

An introduction to a few FP concepts with Elm.

Currying

Functions are curried by default in Elm.

From Wikipedia: "the technique of translating the evaluation of a function that takes multiple arguments (or a tuple of arguments) into evaluating a sequence of functions, each with a single argument".

	require 'json'

	class MyApp
	def call(env)
	request = Rack::Request.new(env)
	headers = {
	'Content-Type' => 'application/json',
	'Access-Control-Allow-Origin' => '*',
	}

	TAX_RATE = 0.4
	BENEFIT_COST = 1000

	SALARY_IN_PENCE = 15_000 * 100

	subtract_benefit = ->(salary) { salary - BENEFIT_COST }
	pay_tax = ->(salary) { salary * (1 - TAX_RATE) }

	calculate_take_home_pay = subtract_benefit >> pay_tax
	puts "Pre-tax benefit: #{calculate_take_home_pay.call(SALARY_IN_PENCE)}"

	import React, { Component } from "react";
	import logo from "./logo.svg";
	import "./App.css";

	const apiSendMessage = message =>
	new Promise((resolve, reject) => {
	const randomDelay = Math.floor(Math.random() * 3000);

	setTimeout(() => {
	const isSuccessful = Math.floor(Math.random() * 10) % 2 == 0;

	// @flow

	class PromiseRetryer {
	fn: () => Promise<*>;
	maxTryCount: number;
	retryDelay: number;
	tries: number;

	constructor(fn: () => Promise<*>, maxTryCount: number, retryDelay: number) {
	this.fn = fn;

	class Result
	def initialize(operation, failure_test, *args)
	@operation = operation
	@failure_test = failure_test
	@args = args
	end

	def and_then(next_operation)
	if failure_test.call(result)
	self

	AWS_REGION=xxx AWS_PROFILE=xxx aws cloudformation list-stack-resources --stack-name xxx \|\
	jq -c '.StackResourceSummaries[] \| select(.ResourceType == "AWS::CloudWatch::Alarm") \| {PhysicalResourceId}'

	class FakeRecord
	# ActiveModel plumbing to make `form_for` work
	extend ActiveModel::Naming
	include ActiveModel::Conversion
	include ActiveModel::Validations

	attr_accessor :foo, :bar

	validates :foo, presence: true