Need help to debug a wired grammar

[Sen Han]

grammar AgencyCompany

  rule expression

    find_agency / find_company

  end

  rule find_agency

    agency space that space concrete_company space work_with

  end

  rule find_company

    company space that concrete_agency space work_with

  end

  rule work_with

    ("has" / "have") space ("partnered" / "partner" / "worked" / "work") space "with"

  end

  rule that

    "that" / "which"

  end

  rule company

    "companies" / "vendors" / "company" / "vendor"

  end

  rule agency

    "agency" / "agencies"

  end

  rule my_company

    "my company"

  end

  rule concrete_company

    entity_name

  end

  rule concrete_agency

    entity_name

  end

  rule entity_name

    (word (space word)?)+ / word

  end

  rule word

    [a-zA-Z]+

  end

  rule space

    [\s]+

  end

end

(Treetop.load "./lib/bgov_brain/queries/agency_company.treetop").new.parse("agency that locked martin has worked with") #=> Works

(Treetop.load "./lib/bgov_brain/queries/agency_company.treetop").new.parse("agency that locked martin abc has worked with") #=> Not Works

(Treetop.load "./lib/bgov_brain/queries/agency_company.treetop").new.parse("agency that locked  has worked with") #=> Not Works

(Treetop.load "./lib/bgov_brain/queries/agency_company.treetop").new.parse("company that dod  has worked with") #=> Not Works

(Treetop.load "./lib/bgov_brain/queries/agency_company.treetop").new.parse("company that department of education  has worked with") #=> Not Works

 

I feel I have a missing concept to understand. 

[Clifford Heath]

Sen,

As soon as your grammar tries entity_name, the repetition of words is unlimited, and consumes the rest of the input.
When your grammar requires other words after that, it will always fail.

Treetop, like other packrat & PEG parsers, will never retry with a reduced number of repetitions.
You must prevent the excessive repetition from occurring, possibly by using a negative lookahead.
In your case it looks like this rule might work:

rule entity_name
(word (space !work_with word)?)+ / word
end

Clifford Heath.

> --
> You received this message because you are subscribed to the Google Groups "Treetop Development" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to treetop-dev...@googlegroups.com.
> To post to this group, send email to treet...@googlegroups.com.
> Visit this group at http://groups.google.com/group/treetop-dev.
> For more options, visit https://groups.google.com/d/optout.

[Sen Han]

Great. Thanks. It works.