Using Elm's Debug Log

Tue, Jan 2, 2018

When starting a small elm project it can be pretty easy to reason about the pieces needed to get the app to compile. One could get pretty far without ever using the Debug.log. However, sometimes with all the compile time errors it comes time to reach into the tool bag for one of Santa’s little helpers. When first getting started I googled around and saw that there was not that many ways to see data inside the elm app. Therefore, I wanted to at least get really familiar with the built in mechanism. I wrote an extremely simple app which echoes out “Y’all” when a button is clicked. The link is at the following.

The syntax when using it in say an update function requires you to set the Debug function equal to an ignore variable _. Being inside a let/in area means that you must return a value for everything called inside of it and then set it to a variable. We don’t really care about the value the call to log returns so the _ works. We also need to be sure to pass a string along with the thing we want to check. This is why we pass in a nice message. Sometimes when I’m in the weeds I will add an extra special message like “log from within HandleFetchCampaigns” to really dial in my logging. I even added a short cut in Spacemacs for adding this logging using yas-snippet. I type C-c C-c C-d and then boom I have a log call set up for my usage. It looks like the following.

# -*- mode: snippet -*-
# name: debug
# key: debug
# binding: C-c C-c C-d
# --
    _ = Debug.log "$1" $1

After I have finished my debugging fun, then I am sure to remove all of them to make sure there are no remnants. Happy debugging my fellow elmers!