Re: false [was: The "Is nil present in a table" problem}

[Tom Wrensch <twrensch@...>]

Hello all,

I've been following the "problems with nil" thread here with great
interest.

It seems as if there are two major problems with the various uses of nil
in Lua: its use in place of a boolean false value, and its use to
represent table members that are not there. Adding a false (and possibly a
true) value to the set of values directly supported by lua would fix only
the first problem.

There is a similar, though somewhat less sever, problem in Smalltalk.
There are times when it is important to differentiate between a variable
that contains a default value and one that contains no value at all. The
solution in Smalltalk/V was to add an EmptySlot class and associated
value.

It may be worthwhile to consider this as a possible solution to the
problem of using nil to show empty slots. This requires some thought:
while adding a new false value and type is a relatively small change to
Lua, splitting nil's use as a default value and empty slot value would
break a lot of code. Maybe someone with more Lua experience can come up
with a way that fits the language better.


  - Tom Wrensch