From: Luke Graham <spoooq@...>
Date: 2005-05-24T15:26:38+09:00
Subject: Re: Multiple return and parallel assignement

On 5/24/05, Michael Ulm <michael.ulm@isis-papyrus.com> wrote:
> Robert Klemme wrote:
> > 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.
> >
> 
> Indeed, strictly speaking, a mathematical function can only have one
> input value. Mathematically, the notation f(x, y) is just a shorthand
> for f([x, y]). If Kernigan and Richie had paid more attention at
> math class we would have declarations like
> 
> (float, float) transform (float, float)
> 
> in C, and the world would be a better place for it :-)

Am I the only one who feels like a curry now?

-- 
spooq