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From: "Joe Hildebrand (jhildebr)" <jhildebr@cisco.com>
To: Bjoern Hoehrmann <derhoermi@gmx.net>, Paul Kyzivat <pkyzivat@alum.mit.edu>
Thread-Topic: [abnf-discuss] How to indent ABNF figures in draft?
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Date: Thu, 3 Jan 2013 17:59:03 +0000
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Subject: Re: [abnf-discuss] How to indent ABNF figures in draft?
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On 1/3/13 10:12 AM, "Bjoern Hoehrmann" <derhoermi@gmx.net> wrote:

>* Paul Kyzivat wrote:
>>And even if that text is considered normative, it isn't entirely clear
>>what is and isn't valid. I *think* it says that the beginning of all
>>rules must be indented the same amount, and continuation lines must be
>>indented more. So that the file could be preprocessed by finding the
>>first non-whitespace line, removing leading whitespace from that line,
>>and then removing identical leading whitespace from all subsequent
>>lines. Then process the result according to the ABNF for ABNF.
>
>That's what I did with http://search.cpan.org/~bjoern/Parse-ABNF-0.05/
>where the documentation notes:
>
>  The ABNF specification disallows white space preceding the left hand
>  side, and so does this module. Remove it prior to passing the grammar
>  e.g. using
>
>    $grammar =~ s/^\s+(?=[\w-]+\s*=)//mg;
>
>  This module does not do that for you in order to preserve line and
>  column numbers. Patches adapting the grammar to allow leading white
>  space welcome.

I did something similar in https://github.com/hildjj/node-abnf, but went
ahead and accepted indented inputs:

    var m = input.match(/^\s+/);
    if (m) {
        var init_ws = m[0];
        input = input.replace(new RegExp("^" + init_ws, "gm"), "");
    }


Line numbers are preserved, and (if I had thought of it) I could add
len(init_ws) to each column offset I report.

Tabs are evil, so you'd get the bad column numbers you'd deserve from
using them. :)

-- 
Joe Hildebrand


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