map/filter/reduce/lambda opinions and background unscientific mini-survey

[Steven D'Aprano]

I said I'd drop the discussion about lambda, but this 
isn't really the same discussion even if it is part of 
the same thread. That's my excuse, and I'm sticking to it.

Terry Hancock wrote:
> On Tuesday 05 July 2005 03:43 pm, Tom Anderson wrote:
> 
>>I understand that the backslash is popular in some ivory-tower functional 
>>languages. Currently, a backslash can be used for explicit line joining, 
>>and is illegal elsewhere on a line outside a string literal, so i think 
>>it's available for this. It would be utterly unpythonic to use puntuation 
>>instead of a keyword, and it would make no sense to novices, but it would 
>>scare the crap out of C programmers, which has to be worth something.
> 
> 
> With list comprehensions and generators becoming so integral, I'm
> not sure about "unpythonic".  And a syntax just occured to me --
> what about this:
> 
> [y*x for x,y]
> 
> ?
> 
> (that is:
> 
> [<expression> for <argument list>]
> 
> It's just like the beginning of a list comprehension or generator, but
> without the iterator.  That implies that one must be given, and
> the result is therefore a callable object.

That is a very long chain of implication:

"It looks like a list comprehension... but there is no 
iterator... so we have to supply an iterator... so it 
takes an argument... so it is a callable object... oh 
and by the way, it can take any arguments, not just 
iterators."

It is also far too easy to make a mistake, eg to write 
something like newlist = [y*x for x,y] when you 
actually wanted the list comp [y*x for x,y in L].

This would create an anonymous function where you 
expected to create a list. It is hard to think of a 
usage case where you didn't discover the error 
reasonably soon, but it would be better for leaving the 
iterator out of a list comp to remain a syntax error, 
rather than produce an unexpected, but legal, object.

Besides, I think Guido should be very cautious about 
introducing new features that use punctuation, instead 
of keywords. We don't want to become perl do we? :-)



-- 
Steven.