The project is born out of constant frustration with certain communities and
their quips that they have functional features, or that there is some new
library that solves all of their problems by doing something functional. The
PHP community seems especially prone to this sort of misinformation, which is
why this project targets that taudry language. It is also somewhat related to
the diatribe on the same topic in my Peave About Map, Reduce and People Who Talk About 'The Functional Style' repo.
In being reminded of the overwhelming interest in the functional style,
I decided to create something as close as possible to a functional DSL in
PHP. This is a bit limited, as PHP does not really have the
ability to support new syntax, so this exercise stops with abstract
syntax. The objective is to concisely show what the closest thing to
functional might be using PHP.
Take a moment to see how this is done. There is what you might call a
two-minute linked list class, meaning that it took all of two minutes or
so to code up, and a few functions that gives it a nudge in the
direction of looking like function evaluation rather than objects. The
normal cadre of basic list functions are implemented, including map
in tail-recursive form. You might note the use of nil for the empty
list. That is because empty is not possible in PHP since it is as built-in
function. Not only is null not possible since it is a PHP type, but
it isn't the correct form of the word for an empty element anyway, nil
is. Please take this code and spread it to the wind,
help educate people on what functional programming actually is, and have
fun with it.
There you have it, now you can say you actually saw something functional in PHP. Facilitated by writing a new abstract syntax DSL in PHP. So it isn't really PHP, it is a new mini-language that is LISP-like. Please take this code and spread it to the wind, help educate people about some of the things that are special about functional programming, and have fun with it. You might find the notes from a presentation I gave helpful. Or you might want to read more about function programming, perhaps starting from one of the fine resources I have listed in this repo.
No, it isn't really functional, in that we don't really have true first-class
or higher-order functions. Yes, it is functional in that the list
processing generates the proper algebra for provable computation. Both of these
are important aspects of a true functional language, but we do what we can. Half of the
problem can be solved with data structures that generally can be implemented in
any language, the other half of the problem is significantly more intrinsic to the the
language in question. The limitation here isn't that we can't use the host language
to define the requisite operations for the algebra, but that we don't have the
ability to handle functions as values as we would with a true functional language.
Next time you hear someone talking about using the functional style or some such
nonesense, please correct them. Unless you are using a language that is pass by
value and you have the structures in place with respect to lists to generate a particular
algebra, you are actually talking about the idea of getting indexing out of indexed
operations. While that is a big improvement in terms of reducing human error, it bears
almost no resemblance to functional programming other than borrowing some of the operator
names.