Re: [Monotone-devel] basic_io inventory

[Christian Ohler]

Thomas Moschny, 2007-04-29:

> On Saturday 28 April 2007, Stephen Leake wrote:
> > Is there some documentation on these requirements for basic_io
> > parsers? I found basic_io.hh and luaext_parse_basic_io.cc; not many
> > comments :). I searched the wiki for "basic_io" and "basic io"; I
> > found BasicIoFormalization, which doesn't say much, but hints at
> > "formal docs" somewhere.
> >
> > It does point to an IRC session, which says that stanzas are not
> > actually meaningful. Which is a scary concept; it implies that in the
> > 'automate inventory' output, the 'path' and 'old_node' lines are
> > _not_ related to each other. Which is of course nonsense!
>
> It is not, because all existing commands emit their output in a fixed order; 
> so the beginning and end of each stanza, and even different types of stanzas 
> can be detected without relying on some amount of whitespace between them, 
> and a stable parser should not (need to) do so.

I don't think this is the only valid way of looking at basic_io. 
Stanzas are separated by an empty line; what's wrong with (or "not 
stable" about) relying on that?  You're suggesting to discard this 
information that is already available at the syntactical level just to 
reconstruct it later at a semantical level.


> Parsing basic_io typically consists of two steps: First, breaking down the 
> input stream into tokens (key tokens followed by zero or more value tokens), 
> thereby striping all white space and dequoting string values. Second, reading 
> the token stream in an application-dependend manner (see above). In this 
> second step, you should have an idea of the meaning and the possible 
> orderings of the key tokens. 

Which basic_io parsers work this way (returning a stream of key/value 
tokens (that does not contain stanza delimiters) instead of a stream of 
stanzas)?

xmtn currently depends on stanzas being separated by an empty line as 
well as on the order of lines within each stanza.

Christian.