Re: Odd behaviour with multiple return values and varargs

[Miles Bader <miles.bader@...>]

I think you're misunderstanding the nature of multiple return values in
Lua, in two ways.

1. I think in general there's a notion that MRVs are "the main RV(s) plus
   some other stuff which you might want to ignore".  This is sort of like
   in common-lisp; contrast it with "rigid" MRVs such as are I guess often
   used with scheme.

   This is essentially a style issue I suppose , but the language
   definitely supports this view -- return values are "flexible" in the
   sense that the system will automatically discard unwanted values (the
   most common case, of course is where the user asks for only one, and
   extra values are discarded), and will even fill in asked-for but not
   supplied values.

2. There's a notion in Lua of unsupplied/non-existant == nil, and one might
   think of every function as having an infinite number of arguments (with
   any unsupplied arguments having the value nil), or of every table as
   having an infinite number of entries (with all non-existing entries
   having a value of nil).  Similarly, one could think of every function
   returning an infinite number of values.

   So the notions of "number of arguments","number of table entries", or
   "number of return values" are kind of shaky, even if such information
   actually is available in some cases, e.g. with select('#',...).

   If we think of a return value sequence as having an implicit
   infinite-number-of-nils at the end, then it's still perfectly natural to
   propagate such a MRV sequence in the last argument position (or as the
   last thing in a table initialization), because the
   infinite-number-of-nils is still at the end.  In any _other_ position,
   it just doesn't work.

   You could make it work if you had (as someone suggested) a "first N
   values" operator, which would let you specify exactly how many values
   from that infinite sequence you wanted.  Currently of course only the
   N=1 case is supported by implicitly discarding all but the first value
   in non-final positions (or by parenthesizing in the final position).

-Miles

-- 
`There are more things in heaven and earth, Horatio,
 Than are dreamt of in your philosophy.'