On Wed, Apr 9, 2008 at 2:41 PM, David Chelimsky <[EMAIL PROTECTED]> wrote:
> On Apr 9, 2008, at 8:13 AM, aslak hellesoy wrote:
>
> > I'm working on a Treetop (http://treetop.rubyforge.org/)
> > implementation of the Story parser.
>
> Hey Aslak, while I love the idea of exploiting treetop for this, this
> would be our first external dependency for end users. That was one of
> the reasons I didn't use treetop in the first place - it had just been
> released and Brian suggested exporing it when I was working on Plain
> Text Stories.
>
> Personally, I'm in support of external dependencies, especially in
> light of recent improvements to Rubygems that make it even easier for
> a gem to manage its own dependencies. But thus far we've had an only
> slightly-less-than-official policy of no external dependencies. Has
> your thinking on this issue shifted as well?
I realize it will introduce a dependency on treetop, but now that
rubygems are ubiquotous and has largely improved with 1.1.0 I think
it's ok. It would only be needed for stories.
A treetop based parser has several benefits:
* Much simpler codebase
* Much better error messages for users. Line numbers and conflict detection.
* Easier integration with other tools (including rspec core)
* Simpler setup for story running (I have a vague plan for that in my head).
I haven't committed the code yet - for now it will live in a separate
repo on GitHub. Here is a teaser for the grammar:
grammar Story
rule story
header narrative scenario*
end
rule header
'Story: ' sentence_line
end
rule narrative
'As a' sentence_line
end
rule scenario
'Scenario: ' sentence_line step*
end
rule step
# The various step rules are generated dynamically
'Given ' (step_1 / step_2)
end
# Dynamically generated rule
rule step_1
'I am ' word ' and ' word
end
# Dynamically generated rule
rule step_2
'I was ' word ' and ' word
end
rule word
([\w])*
end
rule sentence_line
(!eol .)* eol
end
rule eol
"\n" / eof
end
rule eof
!.
end
end
Basically, each run will be based on a core grammar which is extended
by the user, creating extra rules for each parameterised step.
The treetop based parser would create the grammar dynamically, compile
it in-memory and use it to parse plain text stories. My first
benchmarks are pretty good - 0.03 secs to parse/compile the grammar
and less than 0.0001 secs to parse a simple story.
This is fun!
Aslak
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