From: Christopher Genovese <genovese@cmu.edu>
To: emacs-orgmode@gnu.org
Subject: new tag query parser [1/5] -- the motivating issues
Date: Wed, 15 Aug 2012 23:57:04 -0400 [thread overview]
Message-ID: <CAPum5Fg053gQzGgsVjROg1exAbLeYQq5Qw7DjP=-MLiRyYzgBA@mail.gmail.com> (raw)
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My proposed changes in the tag query parser are motivated by the need and/or
desire to do the following. (The example strings work with the new parser.)
1. Combine and modify tag queries programmatically.
The leading case is that a function is given a tag query string and
needs to *exclude* lines matching that query. To do this, we can
transform query strings like so:
"foo+bar+zap/TODO" --> "-(foo+bar+zap/TODO)"
"foo|bar|zap" --> "-(foo|bar|zap)"
The key is that we want to do this programatically while still using
the mapping or agenda search command.^* I use this a lot in my GTD
layer for org; other combinations and transformations come up as well.
2. Write complex queries as simply as possible (i.e., using parens).
Parentheses aren't always necessary, but they can make things nicer.
"(xyz|{^a}-abc) & LEVEL > 1" versus "xyz&LEVEL>1|{^a}-abc&LEVEL>1"
3. Make *fast* heading and priority searches
That information is *already matched* in the current code but access
is not given (or is slow in the case of PRIORITY).
"LEVEL == 2 & HEADING <> {<.*>} & PRIORITY <> \"A\" "
4. Include braces in regular expression matches.
"+{abc\\{{3,7\\}}}" -> regex "abc\\{3,7\\}"
"{[A-Z]+\\S-+{{template}}.*$}" -> regex "[A-Z]+\\S-+{template}.*$"
Because \ escapes are used so heavily in regexex and because strings
require doubling them, using additional \'s would be messy,
ambiguous, and hard to read.
Instead, exploit that we only need to protect {}'s by *doubling*
them: {{ -> { and }} -> }. This is simple, readable, fast, and parity
makes correctness clear at a glance.^**
5. Allow spaces in query strings for readability.
Not a big deal, but easy. See the above examples
6. Get helpful error messages at parse time when there is a problem.
^* It is of course possible to create a matcher from the string
and do the search directly with lower level functions, but
that ends up being a clunky solution.
^** The doubling strategy is also familiar from the doubling of \'s
in quoted strings.
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next reply other threads:[~2012-08-16 3:57 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-16 3:57 Christopher Genovese [this message]
2012-08-18 14:18 ` new tag query parser [1/5] -- the motivating issues Martin Pohlack
2012-08-18 18:10 ` Christopher Genovese
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