pipeline operator may be confusing with bitwise operator.

In this case :
eggs = arg | spam | cheese

Is eggs a composed function or string of bits ?

2015-05-09 21:15 GMT+02:00 Koos Zevenhoven <koos.zevenhoven@aalto.fi>:

On 2015-05-09 21:16, Steven D'Aprano 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)

Apart from the little matter that Guido has said that $ will never be
used as an operator in Python, what is the association between $ and
partial?

Most other operators have either been used for centuries e.g. + and - or
at least decades e.g. * for multiplication because ASCII doesn't have
the × symbol. The barrier to using a completely arbitrary symbol with no
association to the function it plays should be considered very high.

I would only support an operator for function composition if it was at
least close to the standard operators used for function composition in
other areas. @ at least suggests the ∘ used in mathematics, e.g.
sin∘cos, but | is used in pipelining languages and shells and could be
considered, e.g. ls | wc.

My own preference would be to look at @ as the closest available ASCII
symbol to ∘ and use it for left-to-right composition, and | for
left-to-right function application. E.g.

(spam @ eggs @ cheese)(arg) is equivalent to spam(eggs(cheese(arg)))

(spam | eggs | cheese)(arg) is equivalent to cheese(eggs(spam(arg)))

also known as compose() and rcompose().
We can read "@" as "of", "spam of eggs of cheese of arg", and | as
a pipe, "spam(arg) piped to eggs piped to cheese".

For me these are by far the most logical ones too, for exactly the same reasons (and because of the connection of @ with matrix multiplication and operators that operate from the left).

It's a pity we can't match the shell syntax and write:

spam(args)|eggs|cheese

but that would have a completely different meaning.

But it does not need to have a different meaning. You could in addition have:

spam @ eggs @ cheese @ arg   #  equivalent to spam(eggs(cheese(arg)))

arg | spam | eggs | cheese    # equivalent to cheese(eggs(spam(arg)))

Here, arg would thus be recognized as not a function.

In this version, your example of spam(args)|eggs|cheese would do exactly the same operation as (spam | eggs | cheese)(args) :-).

David Beazley has a tutorial on using coroutines in pipelines:

http://www.dabeaz.com/coroutines/

where he ends up writing this:

     f = open("access-log")
     follow(f,
            grep('python',
            printer()))


Coroutines grep() and printer() make up the pipeline. I cannot help but
feel that the | syntax would be especially powerful for this sort of
data processing purpose:

     # could this work using some form of function composition?
     follow(f, grep('python')|printer)

This seems promising!


-- Koos

_______________________________________________
Python-ideas mailing list
Python-ideas@python.org
https://mail.python.org/mailman/listinfo/python-ideas
Code of Conduct: http://python.org/psf/codeofconduct/