RE: [Yaml-core] YAML spec in machine readable format

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On Thu, 2002-12-05 at 04:39, Oren Ben-Kiki wrote:
> Michael G Schwern wrote:
> > (Last one, I swear)
> 
> :-)
> 
> > I was very surprised to find that the canonical YAML spec is written in
> > HTML.  This makes it very, very hard to machine parse and hard to
> > transfer
> > to another format without it coming out looking horrid.
> [...]
> 
> YAML is not an ideal language for "documents". XML is and will remain the
> best choice for that.
> 

I used to think YAML was bad for documents, but then my clever coworker
Lex showed me a few tricks.  Basically, the way to leverage YAML with
more traditional document-oriented languages is to make a very thin YAML
preprocessor:

1) Strings don't get translated at all.
2) Lists/arrays have their elements concatenated.
3) Dictionaries/hashes get expanded by a widget library.

Suppose you start with this document:

<html>
This is <b>bold</b> text.
Imagine lots of other
text here that you're 
comfortable
keeping in HTML.
<table>
<td valign='top' width='47'>foo</td>
<td valign='top' width='47'>bar</td>
</table>
</html>

Suppose that you're comfortable with HTML for inline formatting, but
having to build the tables in HTML is starting to drive you nuts. 
Here's how YAML comes to the rescue:

---
- |
    <html>
    This is <b>bold</b> text.
    Imagine lots of other
    text here that you're 
    comfortable
    keeping in HTML.
- table:
    tds:
        - foo
        - bar
- </html>

You then write a few widgets like this:

def table(data): return '<table>' + widgetize(data) + '</table>'
def tds(data): return ''.join(["<td valign='top' width='47'>" +
widgetize(item) + "</td>" for item in data])

And then you write a little engine that knows to recursively walk your
YAML-driven document specification.  Then engine leaves strings alone,
concatenates lists, and calls to the widget library for dictionaries.

We've generated many thousands of lines of HTML using this approach, and
we're quite happy with it.  Using this approach for the YAML spec, or at
least the POY spec, would be a great way to "dog food" YAML.  It's tasty
dog food!

Cheers,

Steve