vararg asymmetry

["John Belmonte" <jvb@...>]

Usually with Lua programming we discover something new and think, "wow I
didn't realize that could be done".  But sometimes the opposite occurs...

I want an interface for packing/unpacking binary data that works like this:

    data = pack(template, val1, val2, ..., valn)
    val1, val2, ... valn = unpack(template, data)

However as far as I know there is no way to implement unpack in Lua because
the output of a function (that is, the number of values) cannot be generated
by program.  (I do realize that I can just use tables.  Also, I suppose it's
possible to generate the required code on the fly and use dostring but that
is not very reasonable.)  On the other hand, the input of a function can be
generated easily (by making a table and using call) so there seems to be a
lack of symmetry in the standard library.  What I'm trying to do with unpack
is not so bizarre.  In fact the function strfind in the standard library
does the same thing, so it also could not be implemented in Lua.  Maybe
adding a function like this would be useful:

    expand (table)

    Return elements of table with indexes 1..getn(), in order, as individual
values.


-John