Re: [RFC/PATCH v2 1/4] output: Add a new library for plumbing output

From: Julian Phillips <julian@quantumfyre.co.uk>
Date: Apr 13, 2010, 11:46 UTC
Message-ID: <30465b96f3938b1a993ead64bcfb03b0@212.159.54.234>
In-Reply-To: <20100413094351.GA2558@LK-Perkele-V2.elisa-laajakaista.fi>

On Tue, 13 Apr 2010 12:43:51 +0300, Ilari Liusvaara <ilari.liusvaara@elisanet.fi> wrote:

Show 17 quoted lines

> On Mon, Apr 12, 2010 at 12:21:14AM +0100, Julian Phillips wrote:
> 
> I'm writing S-Expression output backend as experiment (not yet even
> sendable
> as WIP) and hit an issue in general framework...
> 
> Also, some comments on documentation...
> 
>> +The output consists of objects, arrays and the actual values, the term
>> item is
>> +used where any of these may be used, and container when either an
>> object or
>> +array may be used.  Objects are unordered collections of named items,
>> and arrays
>> +are ordered collections of unnamed items.  For simplicity a name is
>> always
>> +supplied when creating an item - though it may not always be used

(e.g.

>> if you
>> +are adding the item to a list).
> 
> List? Above says types are 'object', 'array' and 'value'. Then it

defines

> terms 'item' and 'container'. But what is 'list'?

typo - should be array.

>> +* Unstructured Output Functions
> 
> Maybe add extra note about these. When one sees output_token used in

code

> outputting stuff, one can get puzzled until one realizes that token

output

> is ignored for non normal/zero outputs.

Yes. I intend to revist the header and documentation, as they were mostly done before the normal output was added.

Show 13 quoted lines

>> diff --git a/output.c b/output.c
>> new file mode 100644
>> index 0000000..ac8feb1
>> --- /dev/null
>> +++ b/output.c
> 
>> +void output_end(struct output_context *context)
>> +{
>> +	while(context->current)
>> +		output_end_current(context);
>> +
>> +	/*
>> +	 * OUTPUT_NORMAL and OUTPUT_ZERO are special cases - the output

format

>> +	 * is _already_ defined so we have to stick to the rules, we can't

add

Show 6 quoted lines

>> +	 * _anything_
>> +	 */
>> +	if (context->style > OUTPUT_ZERO)
>> +		fprintf(context->file, "\n");
> 
> This is AFAIK really inapporiate for canonical S-Expression output.

Point

> of
> canonical S-Expressions is to have only one way to serialize given tree
> (bit
> for bit identicality) and linefeeds are not allowed except as

serialization

> of linefeed in string.
> 
> Perhaps one could add method/flag to output backend to tell wheither to
> print trailing linefeed?

I think that it probably makes sense to have explicit calls into the backend for start and end rather than assuming that wrapping everything in an object is appropriate, an XML backend for example could then use those callbacks to do XML headers and the outmost element tags etc.

-- 
Julian