Re: [Sbcl-devel] type inferencing in SBCL

[Raymond W. <rw...@gm...>]

(car nil) -> nil, so that's not it. On the other hand, nil is not a number,
so (maybe) one might expect an error to be thrown before the (cond ...).

On Tue, Oct 17, 2017 at 12:49 PM, Will Mengarini <se...@es...> wrote:

> * Jim Newton <jim...@gm...> [17-10/17=Tu 08:29 +0200]:
> >> If B is a number, then A cannot be NIL.   Right?
> >>
> >> (defun test-me (a &aux (b (car a)))
> >>   (declare (type list a)
> >>            (type number b))
> >>   (cond ((null a)
> >>          (format t "line unreachable"))
> >>         ((> 0 b)
> >>          b)))
>
> * Stelian Ionescu <sio...@cd...> [17-10/17=Tu 12:10 +0200]:
> > Looks like you want type CONS.
>
> His point is not that type LIST doesn't exclude NIL; that's
> deliberate.  Instead, he's suggesting that because B is
> initialized from (CAR A), A must /have/ a CAR, therefore
> not be NIL; and the type inference should notice this.
>
> --
>                  Will Mengarini  <se...@es...>
>          Free software: the Source will be with you, always.
> Any sufficiently advanced stupidity is indistinguishable from malice.
>
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