From: Robert Klemme <bob.news@...>
Date: 2005-05-24T01:35:16+09:00
Subject: Re: Multiple return and parallel assignement

Michael Ulm wrote:
> Robert Klemme wrote:
>> Ralph "PJPizza" Siegler wrote:
>>
>>> On Sat, May 21, 2005 at 01:30:13AM +0900, James Britt wrote:
>>>
>>>> Eric Mahurin wrote:
>>>>
>>>>> I've never quite understood why most languages inherently
>>>>> support returning only a single value
>>>>
>>>>
>>>> Conceptual elegance?
>>>>
>>>> Seems cleaner to say that every expression returns an object,
>>>> though that the object may be a container for other objects,
>>>> rather than assert that expressions may return an unknown number
>>>> of objects
>>>>
>>>>
>>>> James
>>>>
>>>
>>> I also think it may be from the original mathematical idea of a
>>> "function', which only has 1 output value for a given set of inputs,
>>
>>
>> Mathematical functions are in no way limited to yielding a single
>> output value.
>>
>
> <pedant_mode>
> But they are. A (mathematical) function  f: M -> N  from a set M to a
> set N is usually defined as a subset of  M x N  such that for each
> element  m in M  there exists exactly one element  n in N  such that
> the pair (m, n) is in the subset; one then writes  f(m) = n.
> </pedant_mode>

So what?  M can be A x B x C and N can be D x E - or whatever.

>>> which 3rd generation programming languages adopted as paradigm.
>>> With multiple return values, more in the mindset of a "relation",
>>> an n to m mapping
>>
>>
>> That's what a mathematical function is basically.  Don't let sin,
>> cos, max, min etc. fool you on this one. :-)
>
> Maybe you are thinking of vector valued functions, where the return
> value is a vector? In that case, one still has only one return value
> (the vector) which in turn contains other elements. This is very
> similar to returning an array in ruby.

With your reasoning there is also just a single input value for math
functions.  So either functions have a single input and a single output
value, or multiple at both ends.  But claiming that there can be multiple
input values but only a single output value is at least a bit dishonest
IMHO.

Kind regards

    robert