Ah, mixing up discussions again. :)
I think what ecmascript does is kind of nice, though a bit late to add to pike: there is a "null" singleton and an "undefined" singleton (and "true" and "false"), and all variables start their life as undefined, unless initialized:
assert( null == null ); assert( null == undefined ); assert( null != false ); assert( null != 0 );
assert( undefined == undefined ); assert( undefined == null ); assert( undefined != false ); assert( undefined != 0 );
Changing not explicitly defined variables to be such an "undefined" value in Pike is bound to break lots of code and do more harm than good for the forseeable future. But I think both of these values would be useful. They are storeable and testable, as seen above (it's a bit crufty, in how that language needs a === comparison operator too, as a few values type coerce, much like how `+ et al behave in Pike, but we would of course not borrow te bad ideas :-).