Ken Okabe ken-okabe

Technical overview

A basic `Option` type

// Option.ts

// definition
export class None {
  readonly tag: 'None' = 'None'

The problem

If a function calls itself recursively then the JavaScript engine has to create a new 'stack' (i.e. allocate a chunk of memory) to keep track of the function's arguments.

Let's look at an example of this happening:

function sum(x, y) {
    if (y > 0) {
      return sum(x + 1, y - 1);

Gistの使い方のメモ

Gistを使い始めて気がついた点をメモした。 Gistはこのようなメモや短いコードをバージョン管理しながら公開するのに便利。

特にこのメモでは、画像を同一ディレクトリに置いて、それGFMファイル内に挿入する方法を解説。

このメモにはgitコマンドの使い方の解説はない。このメモは随時更新される予定。

	{-# LANGUAGE DeriveFunctor #-}
	{-# LANGUAGE LambdaCase #-}

	import Control.Applicative (liftA2)
	import Data.Char
	import Data.Foldable (for_)
	import Data.Functor
	import qualified Data.HashMap.Strict as M
	import Data.List (intercalate)
	import Prelude hiding (any)

	<!DOCTYPE html>
	<html lang="en">
	<head>
	<script type="module">
	import { h, text, app } from "https://unpkg.com/hyperapp"

	app({
	init: () => 0,
	view: state =>
	h("main", {}, [

	//#!/usr/bin/env node --harmony
	/jshint esversion: 6 /
	'use strict';

	// Church numerals in ES6.
	// c.f. https://en.wikipedia.org/wiki/Church_encoding

	// Zero is the identity function.
	let zero = (f => x => x);

	const I = x => x
	const K = x => y => x
	const A = f => x => f (x)
	const T = x => f => f (x)
	const W = f => x => f (x) (x)
	const C = f => y => x => f (x) (y)
	const B = f => g => x => f (g (x))
	const S = f => g => x => f (x) (g (x))
	const S_ = f => g => x => f (g (x)) (x)
	const S2 = f => g => h => x => f (g (x)) (h (x))

	export function flatMap<T, U>(array: T[], callbackfn: (value: T, index: number, array: T[]) => U[]): U[] {
	return Array.prototype.concat(...array.map(callbackfn));
	}

Ken Okabe ken-okabe

Technical overview

A basic Option type

The problem

Gistの使い方のメモ

A basic `Option` type