Re: functions with 'named' arguments

[Dupuis]

Soren Hauberg wrote:
> 
> This thread:
> http://www.nabble.com/Default-arguments-td7869282.html#a7869282 dates
> back to late 2006 where John added support for default arguments. So,
> its been there for some time, but its not used that much.
> 

I played a bit with it and found inconsistencies with regard to R:

function hello (who = "World", closing = "!")
  printf("Hello, %s %s\n", who, closing);
endfunction

octave> hello(who = "Me")
Hello, Me !

octave> hello(closing="and the rest")
Hello, and the rest ! <= 'who' was set; 'closing' takes default value

octave> hello(who = "Me", closing="and the rest")
Hello, Me and the rest

octave> hello(closing="and the rest", who = "Me")
Hello, and the rest Me <= arguments were permuted

would it be possible to have a strict mapping when using the named
parameters paradigm ?

octave> function test(varargin, flag=false)
parse error: syntax error, invalid parameter list

function test(flag=false, varargin)
  printf('flag is %d\n', flag);
  for indi=1:length(varargin), disp(varargin{indi}); endfor
endfunction

octave> test(2, 3, 4, flag=true)
flag is 2
 3
 4
 1

would it be possible
1) to be able to declare named arguments AFTER varargin
2) to ensure the same strict mapping, i.e. unnamed parameters go to
varargin, named ones are matched against the list of named arguments, named
ones without matching being flagged as errors ?

The purpose would be to achieve something similar to:
meanemp<-function(n,...,dist="Uniforme") {
+
switch(dist,Normale=rnorm(n,...),Uniforme=runif(n,...),Exponentielle=rexp(n,...))
+}
meanemp(5, sd=.1, dist="Normale") % normal distrib, 5 samples, mean 0,
standard deviation .1
[1]  0.02443245  0.07669428 -0.11214011 -0.01001278 -0.17726786
meanemp(5, 1, dist="Normale") % normal distrib, 5 samples, mean 1, sd 1
[1] 2.725002  1.775500  2.354803 -0.623507  1.873243

notice that meanemp(5, dist="Normale", 1) and meanemp(dist="Normale", 5, 1)
are identical ways of calling this function 

The mechanism is as follows:
meanemp has a normal parameter, 'n', varargins, '...', and a named argument,
'dist'. Named argument(s) matching the function definition is (are)
extracted from the list, whatever their position. Then normal parameters are
matched based upon their position. The rest becomes varargins, both unnamed
and named, which are passed to daughters functions. There, they are matched
based first upon their name, second upon their position. 

My guess is that this respects to principle of least surprise, delivering
results as the programmer expect them.

Greetings

Pascal
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