PEP 309 (Partial Function Application) Idea

[Steven Bethard]

Chris Perkins wrote:
> Random idea of the day: How about having syntax support for
> currying/partial function application, like this:
> 
> func(..., a, b)
> func(a, ..., b)
> func(a, b, ...)
> 
> That is:
> 1) Make an Ellipsis literal legal syntax in an argument list.
> 2) Have the compiler recognize the Ellipsis literal and transform the
> function call into a curried/parially applied function.
> 
> So the compiler would essentially do something like this:
> 
> func(a, ...) ==> curry(func, a)
> func(..., a) ==> rightcurry(func, a)
> func(a, ..., b) ==> rightcurry(curry(func,a), b)
> 
> I haven't though this through much, and I'm sure there are issues, but
> I do like the way it looks.  The "..." really stands out as saying
> "something is omitted here".

Interesting idea, but I have a feeling that it probably won't fly for a 
couple of reasons:

(1) The existing use of Ellipsis doesn't have anything to do with your 
suggested use.  I think people are generally opposed to giving 
keywords/symbols in Python two very different meanings.  This is one of 
the reasons Guido never liked the "a, b, *c = iterable" syntax.

(2) Emphasis recently on python-dev has been away from syntax changes 
and towards expansion of the standard library.  You would have to make a 
_very_ good case that the new syntax is merited.

Generally I do like the idea -- I think a lot of the cases that people 
have made for keeping lambda could be discarded with something like 
this...  But it'd need an extremely well thought out PEP (and an 
implementation of course) and even then, I wouldn't get my hopes up.

STeVe