Why local symbols are not deleted outside of their scope? For example, if one writes in REPL
and after that
then
It gets part of the symbol-table when the source gets loaded and translated. The Lisp VM only takes care of keeping an environment stack for it. The symbol itself could be used with a different value in another function. Consider the following code:
(let (i 2)
(let (i 3)
(print i))
(print i))
(println i))
If any of the inner scopes would delete the symbol i, the outer scopes would be in trouble.
I do not know is it good, but it gives some supernatural abilities to the symbols.
(lambda()
(if (not symbols1)
(set 'symbols1 (symbols)))
(let ((symbols2
(difference (symbols)
symbols1
'(i symbols1 symbols2 self-conscious-symbols))))
(dolist(i symbols2)
(set i (append "I am " (string i) ". I feel "
(string (apply amb
(difference symbols2
(list i))))
" is close."))))))
(self-conscious-symbols)
(seed (date-value))
(begin (self-conscious-symbols)
(println Sri-Aurobindo)
'(set 'i (list Maharishi
Sri-Chinmoy
Sai-Baba
Dalai-Lama)))
Once out of scope, they evaluate to nil. In fact, testing against a symbol - even one that is unassigned - creates the symbol, too. Remember the differences between variables, values, and symbols. Once out of scope, the symbol has no value and is not a variable anymore.
Symbols are also created in the context when functions are defined within the context.
It confused me at first too, but it is not generally a problem. The symbols being there adds no overhead (in fact, it reduces it when the symbols are reused).
When I was first getting used to newlisp, I wanted it to throw an error if I used a symbol that had never been assigned a value (like Python). I even hacked a bit at the source, but wasn't able to find any easy way. Changing this behavior would probably be a major change to the system, requiring various other parts to change as well.
But this is just one of the many ways (including my wish for a newLint kind of tool) I would like the system to catch me doing dumb things, because I do them a lot.
There is the case when it is necessary to take care about deletition of the variables manually. It is - symbols generated during runtime. Modern PCs can keep, say, millions but not billions of Newlisp symbols in the same time.
I described that in my last blog post - Gensym & Genlet.