What is an Elm Package?

• Elm package repository
• Elm packages enforce SemVer for the public package API
• The SemVer (Semantic Versioning) Spec
• Interesting note: the SemVer spec says breaking changes only refers to the public API. But a core contributor clarifies that breaking changes can come from changes to the public contract that you intend users to depend on. See this GitHub thread.
• list-extra package
• dict-extra package
• Minimize dependencies in your package to make it easier for users to manage their dependencies
• "Vendoring" elm packages (using a local copy instead of doing elm install author/package-name) can be useful in some cases to remove a dependency from your package

Should you publish a package?

• The Elm package ecosystem has a high signal to noise ratio
• Elm packages always start at version 1.0.0
• SemVer has different semantics before 1.0.0 (patch releases can be breaking before 1) - see SemVer spec item 4

Major version zero (0.y.z) is for initial development. Anything MAY change at any time. The public API SHOULD NOT be considered stable.

• Elm package philosophy is to do an alpha phase before publishing package

Keep yourself honest about solving meaningful problems

• Start by asking "What problem are you solving? Who are you solving it for?"

• Scratch your own itch

• elm-graphql

• servant-elm (for Haskell servant)

• Keep yourself honest about solving problems by starting with an examples/ folder

• Early elm-graphql commits started with examples before anything else

• Write meaningful test cases with elm-test

• elm-verify-examples

• Have a clear vision

• Ask people for feedback

• Let ease of explanation guide you to refine core concepts

Make it easy for people to understand your package goals and philosophy

• Include code examples in readme and docs to make it easier for people to get started
• elm-review live stream video
• Use meaningful examples solving concrete problems (images/screenshots are good, too)
• Richard Feldman's Exploring elm-spa-example talk
• Luke's elm-http-builder package
• elm-spa-example's custom http request builder module
• Instead of writing a package, in some cases it could make sense to publish a blog post to share a pattern

Porting libraries vs. Coming Up With an Idiomatic Solution for Elm

• Instead of moment js ported to Elm, have an API built for a typed context
• Ryan's date-format package

How to design an Elm package API

• Define your constraints/guarantees, make impossible states impossible
• Charlie Koster's Advanced Types in Elm blog post series
• Avoid exposing internals of your data
• Elm Radio episode 002: Intro to Opaque Types

Pay attention to how other packages solve problems

• Richard Feldman's talk The Design Evolution of elm-css and elm-test
• Brian Hicks' talk Let's publish nice packages
• Look at prior art, including in other ecosystems
• Look at github issues and blog posts from projects in other ecosystems

Pick your constraints instead of trying to solve every problem

• Helps you choose between tradeoffs
• Having clear project goals explicitly in your Readme makes it easier to discuss tradeoffs with users and set expectations
• Idiomatic elm package guide has lots of info on basic mechanics and best practices for publishing Elm packages

The mechanics of publishing an elm package

• elm make --docs docs.json will tell you if you're missing docs or if there are documentation validation errors
• elm-doc-preview
• Can use elm-doc-preview site to share documentation of branches, or packages that haven't been published yet
• Set up a CI
• Dillon's CI script for dillonkearns/elm-markdown package
• Dillon's elm-publish-action GitHub Action will publish package versions when you increment the version in your elm.json - nice because it runs CI checks before finalizing a new package release
• elm publish will walk you through the steps you need before publishing the first version of your Elm package
• #packages channel on the Elm slack shows a feed of packages as they're published
• #api-design channel on the Elm slack is a good place to ask for feedback on your API design and package idea

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