16: Haskell for greater Elm - JSToElm
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16: Haskell for greater Elm

Haskell for a greater Elm

The more Elm I do, the more I feel like I’m reading a story, and missed a chapter. There feels like some infered knowleadge, that I simply do not possess. Like you missed a key plot point in a movie, and you totally miss the big reveal!

You might be a very visual person. That’s awesome. I am not. I often here hear in teaching, that get the students to get something, anything up on the DOM, as soon as possible. This accomplishs a couple things. It gives them a sense of accomplishment, which is great, sucesses, at every level should be celebrated, but it also gives them some visual feedback, a thing,a tangable thing to look at and manipulate. I am not that type of student. I would rather do 20 commandline println "Hello World than a single visual output. And for me, the reason is repitition. I need the quickest, shortest, black and white feedback. I don’t want to switch applicaitons, I don’t even want to switch window focus. I want to type out a thing, and as quickly as I can, get some regualr text feedback. Like a println, or console.log, anything that does not require me to inspect element.


  • A way of categorizing values
  • ‘a’ :: Char — this reads string ‘a’ has of type Char
  • ’::’ is a type signature, this defines the type for that value, function, expression, whatever it might be.
  • single quotes is a char, but double denotes a string. In JS, it doesn’t matter, the rule is to just be consistant. I feel like JS has given me the room, to either be really sloppy, or to express myself very well?
  • String is a type alias. We use it as a convienance to refer to the actual type. In this case, String is really [Char] a list of Char. We can also use it to denote something like :type Title as
  • infix (++) & concat

    • has the type of list of lists
    • remember a string is just a list of char
    • what’s foldable? [[a]], foldable instances of the Foldable typeclass, to come…
    • if we concat a list of lists, it will simply flatten them into a single list
    • in the below example _ everything to the right of the ’::’ is strictly about our types, not values _ the ‘a’ in the [] is called a type variable _ it does not know(i put cared here, but explicit knowleadge i think is more appropriate) _ it simply doesn’t know, that that it doesn’t care _ it will get a value for ‘a’ during the running of the program at some point, it won’t always be a mystery, then it can be a concrete type like [Char] _ bc the type signature is using a for placeholder of the value to come, it is explicit that the list type must be the same a == a * and the final [a] of the 3 is the return type is also, surprise, a list of a

      Typeclasses provide definitions of operations, or fucntions, that can be shared across sets of types

λ :t (++)
(++) :: [a] -> [a] -> [a]
λ : concat
concat :: Foldable t => t [a] -> [a]


  • Boy, didn’t think I’d see you here. I first learned of you when programming Objc.

    Objective-C polymorphism means that a call to a member function will cause a different function to be executed depending on the type of object that invokes the function

  • Haskell

    1. Parametric polymorphism
    2. Parametric polymorphism refers to when the type of a value contains one or more (unconstrained) type variables, so that the value may adopt any type that results from substituting those variables with concrete types.
    3. Ad-hoc polymorphism
    4. Ad-hoc polymorphism refers to when a value is able to adopt any one of several types because it, or a value it uses, has been given a separate definition for each of those types.

Small Details

  • Things you only get from working with a lang, like the implicit return from a => in JS
  • These are hard to quanitify and communicate, they are rather picked up along the journey.
  • where and let in Haskell introduce local binding to a name. Giving us the ability to reuse it with




Published 7 Dec 2017

A show about learning Elm, Functional Programing, and generally leveling up as a JS developer.
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