Re: [Sbcl-help] string type uncertainty?

[Pascal B. <pj...@in...>]

Christophe Rhodes writes:
> [ off-list to give you a chance to reflect. ]

Thank you :-)=20

> Pascal Bourguignon <pj...@in...> writes:
>=20
> > Christophe Rhodes writes:
> >> Pascal Bourguignon <pj...@in...> writes:
> >>=20
> >> > The point  is that  while a (ARRAY  (ARRAY BASE-CHAR  *) *) has  t=
o be
> >> > implemented as  an (ARRAY T  *), it must  not forget that  it cont=
ains
> >> > actually (ARRAY BASE-CHAR *).
> >>=20
> >> Yes it must.  It is required to by the ANSI standard for the
> >> language.  See the CLHS page for System Class ARRAY:
> >>=20
> >>   If element-type is the symbol *, arrays are not excluded on the
> >>   basis of their element type. Otherwise, only those arrays are
> >>   included whose actual array element type is the result of upgradin=
g
> >>   element-type; see Section 15.1.2.1 (Array Upgrading).
> >
> > Beware, I've always specified the type of the elements. I've only use=
d
> > the * wildcard for the dimension.
>=20
> Perhaps you failed to read the second sentence of the quote?

Yes. You're right.   That's unfortunate.  They link such  a high level
expression  as: (ARRAY  (ARRAY BASE-CHAR  *) *)  to  an implementation
detail  such  as UPGRADED-ARRAY-ELEMENT-TYPE.   This  is without  much
consequence until you treat type declarations as assertions.




So the standard imposes for arrays something like if we said:

   (declare (fixnum 0 10) x)

but because x would be implemented as a signed short anyway, it should
be treated as:

   (declare (fixnum -32768 32767) x)

and: (incf x 30000)  should not raise any exception.



It feels wrong (particularly given that I have today a computer that's
100 times more powerful than 10 years ago when the standard was fixed,
and that there  are enough free cycles in it to  do all the inferences
needed to  do the  right thing),  and I'd move  to ignore  that second
sentence.



(In the meantime, I'll ignore all  notices from sbcl, but I don't like
doing that).

--=20
__Pascal_Bourguignon__                   http://www.informatimago.com/
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Do not adjust your mind, there is a fault in reality.