From: gga <ggarra@...>
Date: 2005-10-24T14:47:01+09:00
Subject: Re: A comparison by example of keyword argument styles


Yukihiro Matsumoto wrote:
> Hi,
>
> Right syntax is
>
>      def function(a, b, c, d:, e: 1, f:)
>      end

So if I have default values on both positional and named parameters, it
would look like this?

       def function( a, b = 2, c = 1, d: 1, e: 2, f: 3)
       end

Hmm...

The reason why pythonist don't need the distinction between
named/positional parameters is that exposing an api also comes down to
common sense.  Let's see if an example works as intended.
To make sure it does, I *won't* say which parameters I expect to be
positional parameters in my api and which one's I already locked.  I
won't provide any rdocs, either.  Let's see if you guess...

       def texture( name, smin, tmin, smax, tmax,
                    filter = 'gaussian', filtersize = 0.5 )
       end

Looking at the above, which parameters would you call by name and which
ones by position?  Spoiler below...
















If you said filter and texture as the named parameters, python's method
probably is on to something.

IMO, parameter default values are so very tighly linked to named
parameters that I almost see no distinction most of the time.  I often
don't see positional arguments with defaults.  The above function, btw,
is not taken from python.  It is taken from probably the oldest api in
existance that has never had a dramatic syntactic change (and where I
first saw what named parameters could do):  Renderman.   This 3d
shading language api has lasted over 20 years without a change and
afaik, they were the first or one of the first languages to have named
parameters.
And yes, before someone points it out, the texture() call in renderman
is more complex than the above, as it automatically reads from globals
and also works with a single parameter and worse, it is overloaded
based on its return values, making it also a perfect counter-example to
the idea of the rule of positional parameters not having defaults.
Let's see how a python guy would solve this issue...

       def texture( name, smin = $s, tmin = $t, smax = $s + $ds, tmax =
$s + $dt,
                    # named parameters:
                    filter = 'gaussian', filtersize = 0.5 )

I added only a single comment... in the middle of the function
definition.
Do I really need the interpreter to enforce the above and have to
rewrite all previously written functions to support named parameters
now?