Articles from Alex Korban

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How to generate JSON from Elm values using Json.Encode

In Practical Elm, I discuss at length how to convert a complex JSON string containing nested objects, arrays and recursion into Elm values.

But what about the opposite conversion, from Elm values to a JSON string? We often need to make requests to a server which include data in JSON format. For example, you might be working with a database like MongoDB or CouchDB, and you might need to get a JSON document from it, modify it in some way, and then send it back to the server.

In JavaScript, conv...

Introduction to the elm/parser package

Do you need to deal with some kind of structured data which is not in JSON format and too complex for regular expressions? Or perhaps you have to validate some kind of complex user input? Or maybe you need to report to users what exactly is wrong with the data?
One of the packages in the Elm core library which can help you with such tasks is elm/parser.
First of all, if you're not familiar with parsing, what is it? A parser allows us to take a string as input and to convert it into Elm values a...

Practical Elm book release date & Elm 0.19 updates

I'd like to give you a couple of updates on Elm 0.19 in this post.

But first, an announcement about my book, Practical Elm for a Busy Developer: I'm going to publish the final release on 18 September.

If nothing else, this will force me to finish the last round of proofreading and tweaks!

I would have liked to finish the book earlier, but I also wanted to make it maximally useful to you, so it took a bit longer. I ended up adding extra content, and the latest draft is over 200 pages. I've ad...

Elm 0.19: details of what's new, how to install/upgrade, reading list

This morning, my Twitter timeline was abuzz with exciting news: Elm 0.19 has been released!

The official announcement focused on the big ticket items: impressive reductions in the size of the generated JavaScript and no less impressive improvements in compilation speed. Those are very good things, but I wanted to provide a more comprehensive list (including some stuff that didn't make it into the release notes either).


Language changes

Nothing major has been added but a few things h...

Learning Elm in 2018: Comprehensive List of Resources

Learning a niche language like Elm involves a lot of head scratching over sparse documentation, posting to forums and hoping to get at least one response, looking at other people's undocumented code on GitHub to solve your problems, and generally a lot of stabs in the dark. Right? Well, I'm happy to say that at least for Elm, it's no longer true.
The official introduction to Elm is a useful overview of the language, but what's available beyond that? In 2018, the answer is "quite a lot", as it t...

Splitting Elm code into multiple files

Have you found it painful to split up your application into modules/pages and to setup the messaging structure correctly? It can be tricky to figure out how to handle Cmds and Msgs across files. And it's still not easy to find examples of how to architect larger apps (and even if you find a large code base, it will be tricky to trace what exactly is going on).

But it doesn't have to be mysterious! What you need is the principles to guide your choices about organising code and splitting it up i...

How Json.Decode.Pipeline chaining works

Json.Decode.Pipeline is a popular package for building JSON decoders. It allows you to build decoders using the forward function application operator (|>) to chain field decoders in a convenient, DSL-like way. For example, we could have a decoder like this:

type alias Node =
{ nodeType : String
, relationName : String
, plans : Plans
, schema : String
, startupCost : Float
, totalCost : Float

decodeNode : Decode.Decoder Node
decodeNode =
decode Node

Practical Elm for a Busy Developer: early access

I’m working on an intermediate level Elm book called Practical Elm for a Busy Developer. I wanted to post a quick note about it for people who are not on my mailing list, since I've just added a huge new section and the book is 70-80% complete now.

I chose not to include the basics (Elm syntax, the Elm architecture etc.) in the book because I think they are adequately covered by other sources. Instead, it will guide you through the practical tasks of creating applications with Elm: building UI...

Json.Decode tricks: decode 8+ fields and nested sub-objects

Suppose you have some JSON that describes map markers:

"name": "Rixos The Palm Dubai",
"lat": 25.1212,
"lon": 55.1535

Using Json.Decode, the decoder for this JSON looks like this:

decodeMarker : Json.Decode.Decoder Marker
decodeMarker =
Json.Decode.map3 Marker
(field "name" Json.Decode.string)
(field "lat" Json.Decode.float)
(field "lon" Json.Decode.float)

If your JSON acquires another field (say, marker color), you need to add one more field decoder ((...

Using modules in Elm

This post is adapted from my book, [Practical Elm for Busy Developers.]

As your Elm code base grows, you will want to start taking advantage of modules to split the code into manageable smaller parts.

In Elm, files and modules have a one-to-one correspondence. If you want to break out a piece of code into a separate file, you have to organise it as a module in that file.

The general approach I would suggest is to start your project with a single file (Main.elm), and keep adding to it until y...