[Rd] question

[ivo welch]

hi gabor:  this would be difficult to do.  I don't think you want to
read my programs.  it would give you an appreciation of what ugly
horror programs end users can write in the beautiful R language  ;-).

clearly, one can work around the lack of such a feature.
multiple-return values are syntax sugar.  but maybe it helps to
explain how I got to my own view.  I had to send an R program to
someone who had never used it before.  without knowing R, he could
literally read the entire program.  the only thing that stumped him
was the multiple return values.  In my program, he saw

  f= function() { return(list(a=myvector1, b=myvector2)) }

  result=f()
  a= result$a
  b= result$a
  rm(result)

I had picked this method up over the years reading r-help.  of course,
I had 10 return values, not two, each return value with its own long
name.  I think it would have been a whole lot nicer if I could have
written FOR HIM simply

  f= function() { return(myvector1,myvector2); }
  (a,b)= f()

again, its syntax sugar.  I would find such syntax a whole lot more
appealing.  and I often write functions that pass back a main program,
but also some debug or other information.  maybe I am the only one...

regards,

/iaw


On Sat, Mar 7, 2009 at 9:28 AM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> Why?   Can you demonstrate any situations where its useful?  Despite
> having my own facility for this I've found that over the years I
> have never used it.
>
> On Sat, Mar 7, 2009 at 9:23 AM,  <ivowel at gmail.com> wrote:
>> Gentlemen---these are all very clever workarounds, but please forgive me for
>> voicing my own opinion: IMHO, returning multiple values in a statistical
>> language should really be part of the language itself. there should be a
>> standard syntax of some sort, whatever it may be, that everyone should be
>> able to use and which easily transfers from one local computer to another.
>> It should not rely on clever hacks in the .Rprofile that are different from
>> user to user, and which leave a reader of end user R code baffled at first
>> by all the magic that is going on. Even the R tutorials for beginners should
>> show a multiple-value return example right at the point where function calls
>> and return values are first explained.
>>
>> I really do not understand why the earlier implementation of "multiple-value
>> returns" was deprecated. then again, I am a naive end user, not a computer
>> language expert. I probably would not even understand the nuances of syntax
>> ambiguities that may have arisen. (this is my shortcoming.)
>>
>> regards,
>>
>> /iaw
>>
>>
>> On Mar 7, 2009 4:34am, Wacek Kusnierczyk
>> <Waclaw.Marcin.Kusnierczyk at idi.ntnu.no> wrote:
>>> Mark.Bravington at csiro.au wrote:
>>>
>>> >
>>>
>>> >> The syntax for returning multiple arguments does not strike me as
>>>
>>> >> particularly appealing.  would it not possible to allow syntax like:
>>>
>>> >>
>>>
>>> >>   f= function() { return( rnorm(10), rnorm(20) ) }
>>>
>>> >>   (a,d$b) = f()
>>>
>>> >>
>>>
>>> >>
>>>
>>> >
>>>
>>> >
>>>
>>> > FWIW, my own solution is to define a "multi-assign operator":
>>>
>>> >
>>>
>>> > '%
>>> >   # a must be of the form '{thing1;thing2;...}'
>>>
>>> >   a
>>> >   e
>>> >   stopifnot( length( b) == length( a))
>>>
>>> >   for( i in seq_along( a))
>>>
>>> >     eval( call( '
>>> >   NULL
>>>
>>> > }
>>>
>>> >
>>>
>>>
>>>
>>> you might want to have the check less stringent, so that rhs may consist
>>>
>>> of more values that the lhs has variables.  or even skip the check and
>>>
>>> assign NULL to a[i] for i > length(b).  another idea is to allow %
>>> be used with just one variable on the lhs.
>>>
>>>
>>>
>>> here's a modified version:
>>>
>>>
>>>
>>>    '%
>>>        a
>>>        if (length(a) > 1)
>>>
>>>            a
>>>        if (length(a) > length(b))
>>>
>>>            b
>>>        e
>>>        for( i in seq_along( a))
>>>
>>>            eval( call( '
>>>        NULL }
>>>
>>>
>>>
>>>    {a; b} %
>>>    # a = 1; b = 2
>>>
>>>    a %
>>>    # a = 3
>>>
>>>    {a; b} %
>>>    # a = 5; b = NULL
>>>
>>>
>>>
>>>
>>>
>>> vQ
>>>
>