elm-compat-019

This is a package for Elm 0.19 that allows you to reach into Elm's past.

You can use some of the old things from Elm 0.17's elm-lang/core or Elm 0.18's elm-lang/core which were changed or dropped in Elm 0.19. Now, the best way to experience all the goodness of Elm 0.19 is to actually modify your code. However, there are cases in which you might want to keep using some "retro" features of Elm 0.17 or 0.18. Perhaps they are handy for your particular scenario, or perhaps you are maintaining some code that you need to compile in multiple versions of Elm.

So, this package may be of some assistance in those scenarios.

API

For the detailed API, see the Elm package site, or the links to the right, if you're already there.

As you will see, the modules from old versions of elm-lang/core with changes that can be ported to Elm 0.19 are included here with the Elm version as a suffix. So, suppose you want to use the old customDecoder from the Elm 0.17 version of Json.Decode, you can do something like this:

import Json.Decode017 exposing (customDecoder)

If you're maintaining some code for both Elm 0.17 and 0.19, then the necessary change is then limited to the import statement -- in the Elm 0.17 version, you'd just change the import to:

import Json.Decode exposing (customDecoder)

One thing which doesn't quite work (but might be nice) is:

import Json.Decode017 as Json
import Json.Decode as Json

The problem is that each has an andThen, so Json.andThen becomes ambiguous.

However, if you're maintaining code for both Elm 0.17 and 0.19, you could do something like the following.

-- In the Elm 0.19 file, use the following imports:
import Json.Decode as Json
import Json.Decode017 as Json17

-- In the Elm 0.17 file, use the following imports:
import Json.Decode as Json
import Json.Decode as Json17

Then, in the body of the either file, when you need something that is specific to Elm 0.17, you can say something like Json17.andThen. In both cases, you'll get the function you want.

If you also want to use some things that are specific to Elm 0.18 or Elm 0.19, you can install Gizra/elm-compat-017 in the Elm 0.17 project, and then do something like this:

-- In the Elm 0.19 file, use the following imports:
import Json.Decode as Json
import Json.Decode as Json18
import Json.Decode017 as Json17

-- In the Elm 0.17 file, use the following imports:
import Json.Decode as Json
import Json.Decode as Json17
import Json.Decode018 as Json18

If you do that, then you can say Json18.andThen or Json17.andThen in either file, and in both cases you'll get the function you expect.

The basic idea is that if you install the appropriate version of Gizra/elm-compat-... for your environment, you should be able to maniuplate your import statements to access any of the function signatures that have been back-ported or forward-ported.

Just to reiterate, none of this is standard operating procedure -- normally, you will be best served by just updating everything to the latest version of Elm. So, this is just for the very few cases where it makes sense to work in multiple versions of Elm at the same time.

Installation

Try elm-package install Gizra/elm-compat-019

Development

Try something like:

git clone https://github.com/Gizra/elm-compat-019
cd elm-compat-019
npm install
npm test