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

[Steven D'Aprano]

On Sun, May 10, 2015 at 12:03:24AM +0200, Gregory Salvan wrote:
> Nobody convinced by arrow operator ?
> 
> like: arg -> spam -> eggs -> cheese
> or cheese <- eggs <- spam <- arg

Absolutely not!

If we were designing a new language from scratch, I might consider arrow 
operators. I think that they are cute.

But this proposal is going to be hard enough to get approval using 
*existing* operators, | __or__ and @ __mat_mul__ (if I remember the 
dunder methods correctly).

To convince people that we should support function composition as a 
built-in feature, using NEW operators that will need the parser changed 
to recognise, and new dunder methods, well, that will be virtually 
impossible. numpy is one of the biggest and most important user bases 
for Python, and it took them something like ten years and multiple 
failed attempts to get enough support for adding the @ operator.

You *might* just have a chance for a -> right arrow operator, just 
barely, but the left arrow <- operator is, I'm pretty sure, doomed to 
failure. The problem is that the parser would need to distinguish these 
two cases:

f<-x   # f left-arrow x

f<-x  # f less than minus x

and I don't think that is possible with Python's parser.



-- 
Steve