long-iglesias-miguel-recursion-with-typeclasses-on-shapeless.md

#Recursion with typesclasses on shapeless

Miguel Iglesias (caente)

http://caente.github.io/

x.ai

Abstract

Shapeless bread and butter is compile time recursion with typeclasses. In this talk I'll explain how I gain intuition to reason about it.

Description

I'll show how to write Find[L,A], where L is an HList, which, similarly to List[A](...).find(f: A => Boolean), will return Some[A] if it has a value of type A, but None otherwise:

("a" :: 1 :: HNil).find[Int] === Some(1)
("a" :: 1 :: HNil).find[Double] === None

Notes

Find[L,A] is a typeclass that I thought I would never need, but software industry is full of uncertainties, and some times you do need an Option[A].

Bio

I've been a back-end engineer at x.ai for two years, focusing mostly on how our robot interacts with the customer; I've been selfish and stayed on the fun part of the job :-) I push my self towards simplicity, but won't shy away from complex/weird methods to achieve it. I try to keep my mind constantly blown, not a hard thing to do once you find functional programming.