Types - Primitive, Named, Phantom, Opaque, Custom, State Machines, and Type Driven Design

[rupert]

Some links to discussion about refinement types and enums in Elm. These are all opaque types but specific applications opaque types.

How to do enums in Elm

TL;DR: I’ve made a working Ellie for this if you want to play around: https://ellie-app.com/nt22pfXCtKa1 I’ve seen a few comments around how working with enums suck in Elm. I believe much of the frustration comes from trying to re-implement in Elm a language feature that exists in other languages. As a result of applying the wrong kind of thinking, the wrong abstraction is reached and Elm gets the blame. So while I’m no expert, the following approach may lessen the pain that some people feel. L…

Elm-Refine: Proposal

Greetings everyone, I’m currently studying computer mathematics at the University of Linz/Austria and am now working on my master-thesis: Refinement types for Elm. In this post I will first explain the main concept and then propose a syntax. I would be grateful if you could give me feedback regarding the syntax. What are Refinement Types? Let’s look at the following example. {-| @refine \int -> int /= 0 -} type alias IntWithoutZero = Int dividedBy : IntWithoutZero -> Int -> Int dividedBy…

Best practice for guarded types?

I’m not actually sure what the best terminology is here, a guarded type, a restricted type? The idea is to wrap a basic type in an opaque custom type, and expose a lower case constructor for it, such that only instances meeting certain guard conditions can ever be created. An example: module Unitary exposing (Unitary, unitary, value) -- Unitary is opaque. {-| Numbers between zero and one. -} type Unitary = Unitary Float unitary : Float -> Maybe Unitary unitary val = if val < 0 then …