Elm on Rails

Transcript

1. Elm on Rails Presented by Brooke Kuhlmann +

2. Overview • A functional language that compiles to JavaScript. •

   A strong focus on simplicity with a concise syntax. • No runtime exceptions (no null or undefined)! • Has a friendly, time traveling, debugger! • Runs on Rails (via the Webpacker gem)! https://elm-lang.org

3. The Benefits of Elm A brief comparison between Elm and

   Ruby. https://elm-lang.org/docs/syntax

4. Elm Lists colors = ["red", "black", "white"] List.head colors --

   Result: Just "red" https://elm-lang.org/docs/syntax#lists colors = [] List.head colors -- Result: Nothing Example 1: Example 2:

5. Ruby Arrays colors = ["red", "black", "white"] colors.first # Result:

   "red" https://ruby-doc.org/core-2.6.3/Array.html colors = [] colors.first # Result: nil Example 1: Example 2:

6. Elm Maybe -- The type definition. type Maybe a =

   Just a | Nothing https://package.elm-lang.org/packages/elm/core/latest/Maybe ℹ No equivalent in Ruby.

7. Elm Records -- Initial record. planet = {name = "Earth",

   isHabitable = True} https://elm-lang.org/docs/syntax#records -- Updated record. updatedPlanet = {planet | isHabitable = False} -- Result: {name = "Earth", isHabitable = False} ℹ All records are immutable by default.

8. Ruby Hashes # Initial hash. planet = {name: "Earth", habitable:

   true} https://ruby-doc.org/core-2.6.3/Hash.html # Mutatation! planet[:name] = "Mars" planet.merge! name: "Mars" # Result {name: "Mars", :habitable: true}

9. Ruby Hashes ⭐ # Initial hash. planet = {name: "Earth",

   habitable: true} https://ruby-doc.org/core-2.6.3/Hash.html # No mutation. updatedPlanet = planet.merge name: "Mars" # Planet: {name: "Earth", :habitable: true} # Updated planet: {name: "Mars", :habitable: true}

10. Elm Type Aliases -- MODEL type alias Planet = {

    name: String, isHabitable: Bool } -- RECORD (function) initialPlanet : Planet initialPlanet = { name = "Planet", isHabitable = True } https://elm-lang.org/docs/syntax#type-aliases

11. Ruby Contracts gem install contracts https://github.com/egonSchiele/contracts.ruby Contract String => String

    => String def label prefix, message "#{prefix}: #{message}" end ℹ Ruby 3.x.x might support this. Requires a gem... ...which then allows for type checking:

12. Elm If Expression https://elm-lang.org/docs/syntax#conditionals -- Record: planet = {name =

    "Earth", isHabitable = True} -- Conditional: if planet.isHabitable then "habitable" else "inhabitable" -- Result: "habitable"

13. Ruby If Statement # Hash: planet = {name: "Earth", habitable:

    true} # Conditional: if planet[:habitable] "habitable" end # Result: "habitable" http://www.rubyist.net/~slagell/ruby/control.html ℹ Has potential to answer a nil.

14. Ruby If Statement ⭐ # Hash: planet = {name: "Earth",

    habitable: true} # Conditional: if planet[:habitable] "habitable" else "inhabitable" end # Result: "habitable" http://www.rubyist.net/~slagell/ruby/control.html Can be enforced by Rubocop.

15. Elm Custom Types -- Single line. type Status = Terraforming

    | Habitable | Barren -- Multiple lines. type Status = Terraforming | Habitable | Barren https://elm-lang.org/docs/syntax#custom-types ℹ No Ruby equivalent.

16. Elm Case Expression toSentence : Planet -> String toSentence planet

    = case planet.status of Terraforming -> "Under construction." Habitable -> "Life is good, stop by!" Barren -> "The humans are dead." https://elm-lang.org/docs/syntax#conditionals ℹ A `_ ->` branch can be used as a catch all (in some situations). planet = {name = "Earth", status = Habitable}

17. Ruby Case Statement case planet.status when :terraforming "Under construction." when

    :habitable "Life is good, stop by!" when :barren "The humans are dead." end http://www.rubyist.net/~slagell/ruby/control.html Planet = Struct.new :name, :status planet = Planet.new "Earth", :habitable

18. Ruby Case Statement ⭐ case planet.status when :terraforming "Under construction."

    when :habitable "Life is good, stop by!" when :barren "The humans are dead." else fail "Unknown planet status." end http://www.rubyist.net/~slagell/ruby/control.html Can be enforced by Rubocop.

19. Elm Functions add : Int -> Int -> Int add

    first second = first + second https://elm-lang.org/docs/syntax#functions add 2 5 -- Result: 7

20. Ruby Methods def add first, second first + second end

    https://www.rubyist.net/~slagell/ruby/methods.html add 2, 5 -- Result: 7

21. Ruby Methods (caveats) # Example 1: def add first =

    0, second = 0 first + second end https://www.rubyist.net/~slagell/ruby/methods.html # Example 2: def add first, second return unless first && second first + second end # Example 3: def add first, second Integer(first) + Integer(second) end

22. Summary • Immutable by default! • Strong types! • No

    runtime exceptions! • No nil! The Magic Tricks of Testing by Sandi Metz (https://www.youtube.com/watch?v=URSWYvyc42M)

23. Elm on Rails Demo!

24. The Elm Debugger Demo! (with a Rails API)

25. Elm Documentation Getting Started • An Introduction to Elm (online

    book) • Functional Programming in Elm (online book, partially complete) Read in order listed. Diving Deeper • Elm in Action by Richard Feldman - Book. $40. • Building Web Apps with Elm by The Pragmatic Studio - Screencasts. $50. • Integrating Elm by The Pragmatic Studio - Screencasts. Free. https://elm-lang.org/docs

26. Elm Community • Slack - Find us in the #boulder

    channel. • Elm Meetup Group - Held at Pivotal Labs. https://elm-lang.org/community

27. Thanks! https://www.alchemists.io