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bug#4136: 23.1; delete-pair
From: |
Eli Barzilay |
Subject: |
bug#4136: 23.1; delete-pair |
Date: |
Sat, 15 Aug 2009 20:00:22 -0400 |
On Aug 16, Juri Linkov wrote:
> >> It seems you and Martin prefer checking against the
> >> `insert-pair-alist' because the function name `delete-pair'
> >> suggests it should be a counterpart of `insert-pair'.
> >
> > ...this is exactly the issue: it is much better if `delete-foo' is
> > always an operation that reverts what `insert-foo' does.
>
> The exact reverse is impossible.
Of course it isn't, but the operation is one that negates in what it
"generally does" the thing that `insert-foo' does. Just like
`scroll-down' and `scroll-up' are opposites even though they don't
always cancel out.
> > The current state of `delete-pair' is so bad that my guess is that
> > hardly anyone used it, so adding another command doesn't make much
> > sense. How about making it do the proper thing (removing only
> > balanced pairs as specified by `insert-pair-alist'), and ignoring
> > errors with a prefix argument?
>
> I've been using `delete-pair' for many years several times a day
> without any problem because my lists are always correctly balanced
> thanks to `insert-pair' that I exclusively use to create balanced
> lists and strings.
Believe me, I've written a paren or two, and I use `insert-pair'
enough to have my own improved version of it. (In fact, guess why I
almost never use smileys in emails.) Still, the first time I tried
this, the cursor was at the beginning of an indented line. But the
point is still the same: having two nearly identical functions is
exactly what prefix arguments are for.
> That's why even in the current state of `delete-pair' it is the
> useful reverse of `insert-pair' because the latter creates balanced
> lists and the former deletes them.
... unless you happen to have your cursor on a non-paren.
> >> This is fixed in the following version:
> >> [...]
> >
> > This version doesn't make much sense as an operation you'd want to do
> > on code:
> >
> > (foo '(x y z))
> > -->
> > (foo 'x y z)
>
> It makes sense when `foo' is a multi-argument function like `list',
> e.g.
>
> (list 'x y z)
>
> So I see no reason to introduce more restrictions to decide what
> parens the user is allowed to delete in his/her code.
You've missed my point: the difference between "y" and "'y" is *huge*,
changing one to the other is something that you don't want to do by
mistake.
On Aug 16, Juri Linkov wrote:
> >> This is fixed in the following version:
> >>
> >> (defun delete-pair ()
> >> "Delete a pair of characters enclosing the sexp that follows point."
> >> (interactive)
> >> (save-excursion
> >> (forward-sexp 1)
> >> (save-excursion
> >> (backward-sexp 1)
> >> (skip-syntax-forward "'")
> >> (delete-char 1))
> >> (delete-char -1)))
> >
> > Still doesn't seem TDTRT with `point' before something like
> >
> > `foo'
>
> I know, I know, after I fix this, you'll come up with another
> test case like
>
> `foo bar'
Those examples are very good IMO -- it's not being picky for nothing,
it's an attempt to avoid nasty surprises that make you end up with
erroneous code. Emacs is usually good at being a careful editor for
code, `delete-pair' is very exceptional in this aspect.
--
((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay:
http://barzilay.org/ Maze is Life!
- bug#4136: 23.1; delete-pair, Eli Barzilay, 2009/08/13
- bug#4136: 23.1; delete-pair, martin rudalics, 2009/08/13
- bug#4136: 23.1; delete-pair, Juri Linkov, 2009/08/13
- bug#4136: 23.1; delete-pair, Eli Barzilay, 2009/08/13
- bug#4136: 23.1; delete-pair, Stefan Monnier, 2009/08/14
- bug#4136: 23.1; delete-pair, Juri Linkov, 2009/08/14
- bug#4136: 23.1; delete-pair, Eli Barzilay, 2009/08/14
- bug#4136: 23.1; delete-pair, Juri Linkov, 2009/08/15
- bug#4136: 23.1; delete-pair,
Eli Barzilay <=
- bug#4136: 23.1; delete-pair, Juri Linkov, 2009/08/16
- bug#4136: 23.1; delete-pair, Eli Barzilay, 2009/08/16
- bug#4136: 23.1; delete-pair, Juri Linkov, 2009/08/20
- bug#4136: 23.1; delete-pair, martin rudalics, 2009/08/20
- bug#4136: 23.1; delete-pair, Juri Linkov, 2009/08/20
- bug#4136: 23.1; delete-pair, martin rudalics, 2009/08/16
- bug#4136: 23.1; delete-pair, Stefan Monnier, 2009/08/20
- bug#4136: 23.1; delete-pair, Juri Linkov, 2009/08/20
- bug#4136: 23.1; delete-pair, martin rudalics, 2009/08/15
- bug#4136: 23.1; delete-pair, martin rudalics, 2009/08/14