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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Parser interface design
Date: Tue, 12 Apr 2011 16:54:24 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2011-04-12T16:54:24-05:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:1ovsbvdul64pw$.1q49g3o7n296m$.dlg@40tude.net...
> On Tue, 12 Apr 2011 16:13:30 +0000 (UTC), Natasha Kerensikova wrote:
>
>> On 2011-04-08, Simon Wright <simon@pushface.org> wrote:
>
>>> 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.
>
> That looks wrong to me. I think that obvious design is to move it to the
> renderer:
>
>   HTML.Emphasize ("bar")  -> "<b>bar</b>"
>   ASCII.Emphasize ("bar")  -> "*bar*"
>   Plain_Text.Emphasize ("bar")  -> "bar"
>   Gtk_Text_Buffer.Emphasize ("bar")  -> sets tags around the text slice
>   ...
>
> Parser just calls On_Emphasize, the implementation of routes it to the
> renderer's Emphasize, which figures out what to do.

Right, that's how it works in the Ada standard formatter tool. The output 
class takes a high-level representation of items and then writes them 
appropriately for the desired output.

                           Randy.