Pointless Style

Point-free considered useful

Posted on 2020-04-06

This should perhaps be called point free style, but I could not resist the pun (and I am not the first) being an occasional consumer of Pointless where pointless things are the most valuable of all. I like pointless style because I like pipelines.

I remember Steve Furber, the chief architect of the original ARM processor, opining of the RISC revolution that the point was that microprocessor architecture had been simplified to the extent that pipelining — executing several instructions concurrently with each instruction being processed in different stages — became feasible. This informs my thinking on pipelines. As an organising principle, they are really powerful.

Point Free

A classic pointy function definition looks like this,

f x = p (q (r (s (t x))))

while in the point-free style it would look like this:

f = p . q . r . s . t

The distinction is that the argument of the function — the point — gets named in the pointy style, but not in the pointless style.

A Real Example

Pipelines can be found everywhere. Take this fragment from the main module of the Hakyll generator used to prepare this blog:

  compile $ pandocCompiler
      >>= loadAndApplyTemplate "templates/post.html"    postCtx
      >>= loadAndApplyTemplate "templates/default.html" postCtx
      >>= relativizeUrls

The compile Hakyll library function takes a monadic value as its argument, which it runs to determine how to prepare a particular kind of blog artefact for publication. The point police could detect an illegal pipeline here and insist that, for readability reasons, this be rewritten in the pointy style.

  compile $ do
    pandocStuffPresumablyHtml <- pandocCompiler
    blahurg <- loadAndApplyTemplate "templates/post.html" postCtx pandocStuffPresumablyHtml
    _wibble <- loadAndApplyTemplate "templates/default.html" postCtx blahurg
    bloggyOutput <- relativizeUrls blahurg
    return bloggyOutput

Well almost, except I have misplaced one of my points for which I am not going to get even a warning.

Hakyll has been beautifully constructed to be accessible to non-Haskellers around an elegant DSL that makes heavy use of pipelines. The user really does not want to be concerned with naming and getting involved with all of the points.

For non-Haskellers.

There is a point to the way of pointlessness!

The Real Problem

I care about readable code and consider readability almost paramount. (I mean within reason, of course.)

The real problem comes when folks try to construct pipelines where there are none, using an incomprehensible jumble of combinators. The problem here is not point-free code but poorly written code.

Got an issue with any of this? Please share or drop me a line (see below).