cscalfani

Type Safe JSON Decoding in Elm

The power of a Static Typed language can seem magical at first. But the goal here is to take a tiny peak behind that curtain.

Elm's implementation of JSON parsing is type safe and how it achieves that can seem like a mystery. Even though I got the code to work, it took me a while to fully understand how it works.

I'm writing it down here for 2 reasons. To help others gain a greater understanding of Types and so I don't forget what I learned.

Word of Caution

szabba

import Html
import Html.App as App
import Html.Attributes as Attributes
import Html.Events as Events
import Json.Decode as Json
import String


main =
    App.beginnerProgram

pdamoc

-- See this document for more information on making Pong:
-- http://elm-lang.org/blog/pong
import Color exposing (..)
import Collage exposing (..)
import Element exposing (..)
import Keyboard
import Text
import Time exposing (..)
import Window exposing (Size)
import Html.App as App

yang-wei

When receiving JSON data from other resources(server API etc), we need Json.Decode to convert the JSON values into Elm values. This gist let you quickly learn how to do that.

I like to follow working example code so this is how the boilerplate will look like:

import Graphics.Element exposing (Element, show)
import Task exposing (Task, andThen)
import Json.Decode exposing (Decoder, int, string, object3, (:=))

import Http

yang-wei

Should be work with 0.18

Destructuring(or pattern matching) is a way used to extract data from a data structure(tuple, list, record) that mirros the construction. Compare to other languages, Elm support much less destructuring but let's see what it got !

Tuple

myTuple = ("A", "B", "C")
myNestedTuple = ("A", "B", "C", ("X", "Y", "Z"))

mgold

module SuperTimer where

import Html exposing (..)
import Html.Events exposing (onClick)
import Time exposing (Time)
import Signal exposing (Address)

type Action = Tick Time | Toggle Bool | NoOp

type alias Model = { running: Bool, count: Float}

JoeyEremondi

-- interface is a more familiar name for the intention of the construct
type alias Append a rest = { rest | append : a -> a -> a}


-- implement is a more familiar name
stringAppend rest = {rest | append = \x y -> x ++ y}

-- this is Monoid
type alias AppendWithId a rest = Append a {rest | id : a}
--                ^ 1 potential superclass

JoshCheek

Learning Elm

What is it? (20 min)

Glance through a few of the examples, maybe 5 or so, to see what kinds of things Elm is doing, what domains they're in, what the code looks like, what other people think Elm is.

manigandham

Strictly Frameworks

• Mobiledoc - github.com/bustle/mobiledoc-kit - framework to build editors with a standardized JSON structure
• ShareDB - github.com/share/sharedb - framework to sync any JSON document using operational transforms, add real-time collaborative editing to anything else
• Bangle.dev - github.com/bangle-io/bangle.dev - toolkit built for building editors, based on prosemirror

Abstracted Editors

These use separate document structures instead of HTML, some are more modular libraries than full editors

jvoigtlaender

module Main where

import Signal
import Time exposing (Time, millisecond)
import String

import Html exposing (..)
import Html.Attributes exposing (..)
import Html.Events exposing (..)
import Effects exposing (Never, Effects)