PEP 309 (Partial Function Application) Idea

[Scott David Daniels]

Reinhold Birkenfeld wrote:
> Steven Bethard wrote:
>>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".

The interaction of this with keyword args and omitted args is
problematic (as is the case for rightcurry, in fact).  I can't
think of a good way to explain what _should_ happen for a
function defined as def function(*args, **kwargs): ... when you:

     def fun(bug, frog, verb): ...
     f1 = function(1, ..., frog=3)
     f2 = f1(..., 4)
     f2()

Keywords were why I did no rightcurry definition in the first place;
I couldn't convince myself there was a good, obvious, resolution.

--Scott David Daniels
Scott.Daniels at Acm.Org