nil isn't as unique in Lua 4.1

[Peter Shook <peter.shook@...>]

I'd rather not have the boolean type because then there will be a need
for functions like Perl's 'defined' (to tell if a variable is not nil)
and 'exists' (to tell if a table has a value for a particular key).  How
else with you be able to tell if a variable is false or nil?

In Lua 4.0, it is simple to delegate to another table:

  x = t1[i] or t2[i]

If element i isn't in table t1, try t2.  But in 4.1, if t1[i] is false,
then this expression will access t2 when you don't really want it to.  I
don't want to see Lua start looking like this:

  $x = exists $t1{$i} ? $t1{$i} : $t2{$i} ;

- Peter