[Python-ideas] Function composition (was no subject)

[Steven D'Aprano]

On Sat, May 09, 2015 at 01:30:17PM -0500, David Mertz wrote:
> On Sat, May 9, 2015 at 1:16 PM, Steven D'Aprano <steve at pearwood.info> wrote:
> 
> > On Sat, May 09, 2015 at 11:38:38AM -0400, Ron Adam wrote:
> >
> > > How about an operator for partial?
> > >
> > >           root @ mean @ map $ square(xs)
> >
> 
> I have trouble seeing the advantage of a special function composition
> operator when it is easy to write a general 'compose()' function that can
> produce such things easily enough.

Do you have trouble seeing the advantage of a special value addition 
operator when it is easy enough to write a general "add()" function?

*wink*

I think that, mentally, operators "feel" lightweight. If I write:

getattr(obj, 'method')(arg)

it puts too much emphasis on the attribute access. But using an 
operator:

obj.method(arg)

put the emphasis on calling the method, not looking it up, which is just 
right. Even though both forms do about the same about of work, mentally, 
the dot pseudo-operator feels much more lightweight.

The same with

compose(grep, filter)(data)

versus 

(grep @ filter)(data)

The first sends my attention to the wrong place, the composition. The 
second does not.

I don't expect everyone to agree with me, but I think this explains why 
people keep suggesting syntax or an operator to do function composition 
instead of a function. Not everyone thinks this way, but for those who 
do, a compose() function is like eating a great big bowl gruel that 
contains all the nutrients you need for the day and tastes of cardboard 
and smells of wet dog. It might do everything that you want 
functionally, but it feels wrong and looks wrong and it is not in the 
least bit pleasurable to use.



-- 
Steve