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bug#7151: `set-marker' narrowing and proposed feature `buffer-narrowed-p
From: |
MON KEY |
Subject: |
bug#7151: `set-marker' narrowing and proposed feature `buffer-narrowed-p' |
Date: |
Sat, 2 Oct 2010 14:12:03 -0400 |
`set-marker' can not be set beyond value of `point-max'
This is documented here:
,---- (info "(elisp)Moving Marker Positions")
|
| If POSITION is less than 1, `set-marker' moves MARKER to the
| beginning of the buffer. If POSITION is greater than the size of
| the buffer, `set-marker' moves marker to the end of the buffer.
| If POSITION is `nil' or a marker that points nowhere, then MARKER
| is set to point nowhere.
|
`----
Some mention in the above section should be made of `buffer-size' so users can
now how to check if the buffer is narrowed.
Likewise, docstrings of `>', `<', `<=', `>=', all indicate their arguments:
,----
|
| Both must be numbers or markers.
|
`----
There is a discrepancy here in that the following signals an error:
(let ((mk-mrk (make-marker)))
(set-marker mk-mrk nil)
(> mk-mrk (point-max)))
;=> (error "Marker does not point anywhere")
Moreover, as the docstring of `set-marker' doesn't indicate that its range is
bounded by the current values of `point-max' and `point-min' simple arithmetic
checks for a markers value against some arbitrary buffer position can lead to
confusing return values:
(let ((mk-mrk (make-marker)))
(progn (narrow-to-region (+ (point-min) 10) (- (point-max) 10))
(set-marker mk-mrk (1+ (point-max)))
(widen))
`(,(= mk-mrk (point-max))
,(>= mk-mrk (point-max))
,(< mk-mrk (point-max))
,(marker-position mk-mrk)
,(point-max)))
;=> (nil nil t <PSN> <PSN>)
(let ((mk-mrk (make-marker)))
(set-marker mk-mrk (1+ (point-max)))
(> mk-mrk (point-max)))
;=> nil
(let ((mk-mrk (make-marker)))
(set-marker mk-mrk 12000)
(> mk-mrk (point-max)))
;=> nil
(let ((mk-mrk (make-marker)))
(set-marker mk-mrk 12000)
(= (marker-position mk-mrk) 12000))
;=> nil
(let ((mk-mrk (make-marker)))
(set-marker mk-mrk (1+ (point-max)))
(> mk-mrk (1- (point-max))))
;=> t
I think some mention of these anomalies should be made in the respective docs in
addition to the scattered lisp service provided by the manual.
I would also like to propose addition of a new function `buffer-narrowed-p'.
rgrep'ing buffer-narrowed-p in "lisp/" did not return any results...
(defun buffer-narrowed-p (&optional buffer-or-name)
"Test if buffer narrowing is in effect.
When optional arg BUFFER-OR-NAME is non-nil check for narrowing in that buffer
instead. Default is `current-buffer'.\n
:EXAMPLE\n\n\(prog2
\(narrow-to-region \(line-beginning-position\) \(line-end-position\)\)
\(buffer-narrowed-p \"*Help*\"\)
\(widen\)\)\n"
(let ((chk-bffr (if buffer-or-name
(or (get-buffer buffer-or-name)
(error "Optional arg BUFFER-OR-NAME does
not find buffer: `%S'"))
(current-buffer))))
(with-current-buffer chk-bffr
(or (> (point-min) 1)
(/= (buffer-size) (1- (point-max)))
(/= (- (point-max) (point-min)) (buffer-size))))))
--
/s_P\
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MON KEY <=