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From: Natasha Kerensikova <lithiumcat@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Parser interface design
Date: Tue, 12 Apr 2011 16:13:30 +0000 (UTC)
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Date: 2011-04-12T16:13:30+00:00
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Hello,

On 2011-04-08, Simon Wright <simon@pushface.org> wrote:
> Natasha Kerensikova <lithiumcat@gmail.com> writes:
>
>>> Don't see what's wrong with providing a No_Op function which returns its
>>> input unchanged? unless you do something specific for a null?
>>
>> Yes, as I said in my reply to Dmitry, I thought of disabling in the
>> parser the feature associated to a callback set to null. In the
>> "foo *bar* baz" example I provided, using a No_Op for Emphasis would
>> result in "<p>foo  baz</p>", while disabling the emphasis feature means
>> considering the star as an inactive character, resulting in
>> "<p>foo *bar* baz</p>".
>
> I had in mind more that using my No_Op (I think it was Georg who used
> the better name Identity) would result in "<p>foo bar baz</p>".

Indeed, and this is *not* the result I want: if the star is supposed to
be a character like any other (and not the indicator of emphasis), then
it should be in the result too: "<p>foo *bar* baz</p>".

> In other words, HTML.Emphasize ("bar") would return "<b>bar</b>", but
> No_Op ("bar") would just return "bar".

And that's exactly why disabling emphasis should be done on the parser
level: the callback only has the semantic information ("render bar
emphasized") without any knowledge of how it was obtained (the source
could have been "foo *bar* baz" or "foo _bar_ baz"). Therefore no
callback can reconstruct the intact input.


Natasha