#+title: Abstractions; Haskell vs Clojure
#+subtitle: How are both Haskell and Clojure good to capture some abstractions
#+date: [2020-01-18 Sat]
#+created: [2020-01-18 Sat]
#+author: Yann Esposito
#+EMAIL: yann@esposito.host
#+keywords: Haskell Clojure functional-programming
#+DESCRIPTION: Simulate some abstractions in Clojure vs Haskell
#+OPTIONS: auto-id:t toc:t
#+STARTUP: overview

#+begin_notes
This is a short essay to try to find if Haskell is as limited in its
abstractions power as I experienced many times when learning it.
Now I've got a lot more experience in Haskell and in Clojure.
I would like to see if I'll be able to manage to put some abstractions in
Haskell and in Clojure.
#+end_notes

* Abstractions
:PROPERTIES:
:CUSTOM_ID: abstractions
:END:

The notion of abstraction is generally not pretty well defined.

For example, not using pointer can be considered an abstraction.
Garbage collection is an abstraction.
Procedures are an abstraction.
ORM are an abstraction.
Monads are an abstraction.
Objects and Classes are an abstraction.

I would be surprised is not anyone has made a kind of hierarchy to organize
different abstractions as they seems to me of different nature.

In this post I will only focus on those few abstractions:

- Object Oriented Programming (Objects and Classes, inheritence, etc...)
- Frameworks for managing the lifecycle and dependencies of software
  components with have runtime state (in Clojure: Component or Trapperkeeper)
- ORM/Store abstractions

* Object Oriented
:PROPERTIES:
:CUSTOM_ID: object-oriented
:END:

So in Clojure, this is quite straightforward if you consider you are
authorized to use the underlying language (java).

** Haskell
:PROPERTIES:
:CUSTOM_ID: haskell
:END:

Notion of Object, something that contain an inner state + some methods.
Notion of Class, a boilerplate for creating new Objects.

#+begin_src haskell
newtype MethodName = MethodName Text
data Object s m = Object { state :: s
                         , methods :: forall a. MethodName -> s -> a }
#+end_src

hmmm.... At the very begining of trying to write it down, it already suck...