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bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th e
From: |
MON KEY |
Subject: |
bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element |
Date: |
Fri, 20 Aug 2010 14:44:12 -0400 |
On Fri, Aug 20, 2010 at 9:02 AM, Stefan Monnier
<monnier@iro.umontreal.ca> wrote:
>> As you wish. Though, I don't think changing the wording solves the
>> real problem If there are no good reasons to create a boole-vectro of
>> length 0 why allow it?
>
> That's the wrong question. The question is: why not allow them?
How about Juanma's example earlier wich is a mis-application of substring on
vectors satisfying the predicate `bool-vector-p' e.g. his:
> (defun split-vec (v p)
> (list (substring v 0 p)
> (substring v p (length v))))
>
>> Emacs lisp doesn't and I can think of no good reasons to create 0
>> length bool-vectors.
>> Can any one else?
>
> The same reasons to create zero-length strings.
>
I'm not convinced.
Anyhow, my query included the caveat "good reasons" :)
(substring (make-bool-vector 0 t) 0)
;=> Debugger entered--Lisp error: (wrong-type-argument arrayp #&0"")
And, it doesn't really work for vectors either:
(substring (make-vector 0 1) 0)
;=> []
Likewise, where is the sense in these:
(apply 'string (append (make-bool-vector 0 t) nil))
;=> ""
(concat (make-bool-vector 0 t))
;=> ""
When this:
(concat)
;=> ""
and this:
(apply 'string nil)
;=> ""
would suffice.
Note, I _do_ recognize that there is some utility for things like this w/
_vanilla_ vectors:
(defmacro v->empty (&optional char-val-maybe)
(let ((vvoid (make-symbol "vvoid")))
`(let ((,vvoid (if (characterp ,char-val-maybe)
1 0)))
(make-vector ,vvoid ,char-val-maybe))))
(v->empty 'not-a-char)
;=> []
(v->empty 32)
;=> [32]
(v->empty)
;=> []
(mapconcat #'identity
(mapcar #'(lambda (ve) (concat (v->empty ve)))
'(119 'not-a-char 32 nil 111 'nor-inil
32 "nope" 119 'nada 33)) "")
But I can't see how the `make-vector' idiom would translate for
`make-bool-vector'.
> Stefan
>
--
/s_P\
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, (continued)
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, Chong Yidong, 2010/08/19
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, MON KEY, 2010/08/19
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, Juanma Barranquero, 2010/08/19
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, Chong Yidong, 2010/08/19
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, MON KEY, 2010/08/19
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, Juanma Barranquero, 2010/08/19
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, MON KEY, 2010/08/20
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, Juanma Barranquero, 2010/08/20
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, MON KEY, 2010/08/20
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, Stefan Monnier, 2010/08/20
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element,
MON KEY <=
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, Kevin Rodgers, 2010/08/21
- bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, Andreas Schwab, 2010/08/21
bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, MON KEY, 2010/08/21
bug#6878: bool-vectors of length 0 signal error when aref/aset the 0th element, Andreas Schwab, 2010/08/18