Everything Is Just Functions: 1 week with David Beazley and SICP

They give a nice introduction to encoding state as pure functions. In fact, there are many more purely functional encodings for all kinds of data like trees, integers, sum/product types, images, monads, ...

The encodings can be a bit confusing, but really elegant and tiny at the same time. Take for example a functional implementation of the Maybe monad in javascript:

  Nothing = nothing => just => nothing
  Just = v => nothing => just => just(v)
  
  pure = Just
  bind = mx => f => mx(mx)(f)
  
  evalMaybe = maybe => maybe("Nothing")(v => "Just " + v)
  console.log(evalMaybe(bind(Nothing)(n => pure(n + 1)))) // Nothing
  console.log(evalMaybe(bind(Just(42))(n => pure(n + 1)))) // Just 43

[flagged]

I think it's all right if you're used to the notation. The first two lines are tagged unions and will be recognisable as such if you're familiar with encodings like Scott/Church pairs/lists/numbers. Once you understand the structure, the definition of `bind` becomes obvious, as its two arguments represent the cases "is nothing" and "is just", where in the first case Nothing is returned, and in the second case the function is applied to the value inside the Just.

I think that writing such code, if only for educational purposes, can be really helpful in actually understanding how the state "flows" during the monadic bind/return. Typical monad instantiations of Maybe do not give such deep insight (at least to me).

> Just because you can do a thing doesn’t mean you should.

Of course you should, where would be the fun in that?

It's alright once you get used to it usually means it isn't alright in my experience. There are exceptions of course.