[luatex] String manipulation in Lua.

Paul Isambert zappathustra at free.fr
Fri Dec 3 12:28:09 CET 2010

Le 03/12/2010 12:08, Philipp Gesang a écrit :
> On 2010-12-03<10:37:02>, Paul Isambert wrote:
>> Le 03/12/2010 00:22, Philipp Gesang a écrit :
>>> If you encounter problems with magic characters in patterns,
>>> there is some assistance waiting in the context helper libs:
>>> http://wiki.contextgarden.net/String_Manipulation#string.escapedpattern.28string.29_.7C_string.partialescapedpattern.28string.29
>> Are you trying to lure me into ConTeXt? :)
>> Nice to get inspiration from, though.
> Well, not *actively* so -- but it would appear that context of
> itself has some involuntarily alluring property that does the job
> pretty well.

ConTeXt has tons of ``involuntarily'' alluring properties anyway, 
besides string manipulation. As far as I'm concerned, though, it has one 
big drawback: I didn't write it. So when I want it to stop doing this or 
that, I can't just fix some lines of code. Ok, now you might tell me: 
you'll never want ConTeXt to stop doing this or that, because it is so 
good -- but you don't know the level of perversion I sometimes reach :)

>>> PS: What’s the problem with lpeg, anyways?
>> Nothing, but I don't know how to use it and it seems to me it can't
>> be used lightly; and for the moment I have other things to do.
>> Your code, for instance, which seems to involve a so-called grammar,
>> looks really interesting, except I don't know what lpeg.Cmt,
>> lpeg.Cs, etc., mean, so to me it's unreadable. [Ok, from what I can
>> read, it does the same thing as the above function.]
> “Cs” triggers “smooth” substitution inside its scope. Without it
>      you would get a lose bunch of substitutes missing the rest of
>      the string in between.
> “Cmt” gives you free hand to create your very own personalized
>      matching function -- it does match, if the pattern it
>      encounters is matched by the first argument, but also checks
>      if the second arg -- the function -- returns true. This makes
>      it the most versatile of any of lpeg’s functions (not
>      omnipotent, though …) as you can feed it arbitrary conditions
>      (imagine patterns that match only on Mondays, call a routine
>      to check your bank account before matching, or match iff
>      there is an entry in an online dictionary for the match as
>      filtered through an md5 function …).
>      (Details at Roberto’s: http://www.inf.puc-rio.br/~roberto/lpeg/lpeg.html)
> Wrapping things up in a grammar saves rules which can become
> necessary in bigger patterns (have a look at
> http://lua-users.org/lists/lua-l/2008-11/msg00470.html) but in
> this case you could do without it.
> Switching to lpeg means freeing yourself from the limitations
> (and idiosyncratic notation) of the common string patterns. It
> surely *can*, as you put it, be used lightly once you got the
> hang of it.

The problem is precisely getting the hang. Actually I'll switch to lpeg 
one day or another. I understand not using it is like sticking to 
\lastbox to analyze a paragraph, but for the moment I want something 
done that'll make do with the basic string functions. But thank you, the 
code you gave will be a good place to start to understand it (I don't 
know why, I have a very low tolerance threshold to Roberto's lpeg page; 
I find it extremely interesting for 15 minutes, then get upset...).


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