Re: Why not a setf-able NIL ?

kodifik@xxxxxxxxxxxxx wrote:
As we all know, in Common Lisp logical falsehood is represented by the
non-symbolic atom NIL, which in turn happens to be also the empty list
'().
Everything not nil is true, so in lisp 0 is true.
If -however- NIL were a symbol, one could program things like (let
((nil 0)(number iterations)) (loop while number..) which would
simplify code very often, as the C dudes quickly noticed.
1- I wonder whether there is some really important (theoretical)
reason for not making NIL setf-able, aside implementation simplicity
or speed considerations (practical reasons).
Of course, the programmer would have then to keep in mind that (cons a
nil) could no longer yield (a), and things like that. In other words:
the language would be much more powerful with a redefinable falsehood,
but with greater power comes greater responsibility.
2- Actually, the very fact that the reserved word NIL exists seems to
suggest that this possibility was once regarded.


(loop until (zerop number) ...)


Pascal

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