My experience upgrading to Elm 0.19

Elm is unstable, so upgrading to the next version can be painful. Here’s what I needed to do to upgrade from 0.18 to 0.19.

• Replace elm-package.json and tests/elm-package.json with elm.json – e06f5a1728
• Switch to the new elm-test – b964b7c7a
• Re-arrange Main, and how we call it from JavaScript – 0c118c49f
• Stop using eeue56/elm-all-dict (since it’s not ported to 0.19 and porting it looked hard due to a lack of Debug.crash) – fe100f256
• Replace toString with String.fromX or Debug.toString – 9e78163d0a3
• Stop “shadowing” names by making new variables with the same name as another in the scope – 9688a621de
• Adapt to the changed Html.style function – b991ab4f
• Stop using Debug.crash – f98a70ad1
• Adapt to the changes in the Regex module – 856762a4
• Stop using tuples with more than 3 parts – 472c0bb7

The lack of Debug.crash is really, really painful, especially for a library like eeue56/elm-all-dict that has lots of invariants that are hard or impossible to enforce via the type system. On the other hand, if Elm can give a hard guarantee that there will be no runtime errors, this seems pretty cool. The problem is that some code may well have to return the wrong answer silently, instead of crashing, which could be much worse than crashing in some use-cases.

I was annoyed by the lack of more-than-3-part tuples, but even as I did the work to change my code, I saw it get better, so it’s hard to argue with.

The hardest part to work out was how to run the tests. Fortunately the tests themselves needed almost no changes. I just needed to do this:

rm -r tests/elm-stuff
rm tests/elm-package.json
sudo npm install -g elm-test@0.19.0-beta8
elm-test install
elm-test

My next job is to check out the –optimize compiler flag, and the advice on making the code smaller and faster.