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".
It's a pity we can't match the shell syntax and write:
but that would have a completely different meaning.
David Beazley has a tutorial on using coroutines in pipelines:
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)