032: Elm's Universal Pattern

Joël Quenneville (Twitter)Joël's blog post Elm's Universal Patternmap2Maybe.map2MetaphorsSome common metaphors for Elm's Universal Pattern (Applicative Pattern).MappingCombiningLiftingWrapping and unwrapping boxesBlog post on Two ways of looking at map functionsExamplesRandom generatorsApply mapping functions to vanilla value functions to keep things cleanTipsSeparate branching code from doing code (discussed in-depth in Joël's blog post Problem Solving with Maybe)Stay at one level of abstractionJson decoders as combining functionsScott Wlaschin Railway Oriented ProgrammingDillon's blog post Combinators - Inverting Top-Down TransformsThe JSON structure and Elm type don't have to mirror each other - start with your ideal type and work backwardsApplicative patternApplicative needs 1) way to construct, 2) map2 or andMapJson.Decode.Pipeline.required functionRecord constructorsPractice writing it with an anonymous function to convince yourself it's equivalentRecord constructors are just a plain old elm functionmap2 doesn't take a type, it takes a function -NoRedInk/elm-json-decode-pipeline is a useful reference for implementing this kind of api on your ownApplicative Laws in HaskellMonomorphic vs polymorphicParser Combinatorselm/parser episodeJoël's blog posts on the ThoughtBot blogJoël's Random generators talkJoël's Maybe talkSome more blog posts by Joël that related to Elm's Universal Pattern:Running out of mapsPipeline Decoders in ElmJoël's journey to building a parser combinator:Nested cases - https://ellie-app.com/b9nGmZVp9Vca1Extracted Result functions - https://ellie-app.com/b9qtqTf8zYda1Introducing a Parser alias and map2 - https://ellie-app.com/b9MwZ3y4t8ra1Re-implementing with elm/parser - https://ellie-app.com/b9NZhkTGdfya1Getting Unstuck with Elm JSON Decoders - because mapping is universal, you can solve equivalent problems with the same pattern (described in this post)