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From: | Lennart Borgman (gmail) |
Subject: | Re: Idea for syntax-ppss. Is it new? Could it be any good? |
Date: | Sun, 27 Jul 2008 02:36:26 +0200 |
User-agent: | Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.9) Gecko/20071031 Thunderbird/2.0.0.9 Mnenhy/0.7.5.666 |
Alan Mackenzie wrote:
Hi, Emacs, Looking at the doc string for syntax-ppss, it seems this could be _very_ useful in a certain body of code I'm responsible for. That body of code has a lot of heuristics that determine whether point is within a string/comment, and some of these are not watertight (such as hard-coded limits on comment sizes to achieve speed). Basically, they're a PITA. syntax-ppss, if it was guaranteed watertight, could remove the gnawing uncertainty from much of the code. However, the manual documents limitations on syntax-ppss's functionality. How about reimplementing it thusly?: The current syntax would be cached for positions at every N bytes (where N would be, perhaps 1024, possibly 8192). A call to syntax-ppss would simply call parse-partial-sexp from the latest valid cached position, filling out the cache as it goes. Any buffer change would invalidate cached values for N > POS.
There are some defadvices for syntax-ppss and cousins in mumamo.el that does something like this. This is needed in multi major mode buffers if the normal font lock routines is used there.
I do not exactly do what you propose and a bit more is needed (for mumamo). I think however that any solution should take the need for multi major modes into account.
I envisage coding this in C rather than Lisp. There would be some complications to do with making sure the syntax table isn't tampered with, and so on. This code would surely be fast and reliable. Obviously I'm not proposing this for the pending release, but what do people think about the idea?
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