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//invaluable for all those Choice<'a, exn> flows
let exnf f = Printf.ksprintf (fun s -> exn s) f

//combine paths
let (</>) x y = System.IO.Path.Combine(x, y)

//allows you to pattern match on values in the current scope rather than just literals
let (|Eq|_|) expected value =
    if expected = value then Some ()
    else None

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// This is am example of an immediate write / random access cursor for Excel with basic formatting options.
// Implementation is based on a concrete, non generic writer monad with no payload ("do!"" only) (only state).
// Instead of directl writing to excel, an alternatives would be a random acces to a 
// copy-on-write list (or even a mutable array) and then bulk-write the result to excel in one shot.
// When only forward access would have been required, a simple seq expression with yields would have been enough.
// Anyway, it is a demonstration on how to "hide" pseudo-mutable state that is passed through a computation.
// 
// I personally use it for generating reports based on various data sources.

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:: Sleep for N seconds:

ping localhost -n N -w 1



:: Get the date and time (US LOCALE ONLY)

set YEAR=%DATE:~-4,4%
set TWOYEAR=%DATE:~-2,2%

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namespace MyNamespace

type IMyInterface =
    abstract GetValue: unit -> string

type MyRecord = 
    { MyField1: int
      MyField2: string }
    interface IMyInterface with
        member x.GetValue() = x.MyField2

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{
    "version": "0.1.0",
    "command": "cmd",
    "args": [
        "/c"
    ],
    "showOutput": "always",
    "echoCommand": true,
    "tasks": [
        {

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Architecture

• Use Onion architecture

  • Dependencies go inwards. That is, the Core domain doesn't know about outside layers

• Use pipeline model to implement workflows/use-cases/stories

  • Business logic makes decisions
  • IO does storage with minimal logic
  • Keep Business logic and IO separate

• Keep IO at edges

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{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Example",
      "type": "node",
      "request": "launch",
      "runtimeExecutable": "node",
      "runtimeArgs": ["--nolazy", "-r", "ts-node/register/transpile-only"],

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React - Functional error boundaries

Thanks to React hooks you have now happily turned all your classes into functional components.

Wait, all your components? Not quite. There is one thing that can still only be implemented using classes: Error boundaries.

There is just no functional equivalent for componentDidCatch and deriveStateFromError yet.

Proposed solution

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Transcript from Outside-In TDD

• part 1
• part 2
• part 3
• Bank Kata

Part 1

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// 3D Dom viewer, copy-paste this into your console to visualise the DOM as a stack of solid blocks.
// You can also minify and save it as a bookmarklet (https://www.freecodecamp.org/news/what-are-bookmarklets/)
(() => {
  const SHOW_SIDES = false; // color sides of DOM nodes?
  const COLOR_SURFACE = true; // color tops of DOM nodes?
  const COLOR_RANDOM = false; // randomise color?
  const COLOR_HUE = 190; // hue in HSL (https://hslpicker.com)
  const MAX_ROTATION = 180; // set to 360 to rotate all the way round
  const THICKNESS = 20; // thickness of layers
  const DISTANCE = 10000; // ¯\\_(ツ)_/¯