Parser infinite loop

[Will Myers]

Hi, All

Hoping to get some help as my parser keeps deadspinning. 

I'm trying to parse a Latex document into HTML markup. So far I'm starting simply, I just want to parse an input with `tags` and `text`. When I start the following grammar using :root => :paragraph, I get an infinite loop with the following input:

'friend \emph{hello}\n\n'

It seems to be stalling at the first '\n' character. I've been building the grammar into a .rb file and debugging but can't seem to work out why it can't escape. 

grammar Latex

  rule document

    (paragraph)* {

      def content

        [:document, elements.map { |e| e.content }]

      end

    }

  end

  rule paragraph

    ( tag / text )* eop {

      def content

        [:paragraph, elements.map { |e| e.content } ]

      end

    }

  end

  rule text

    ( !( tag_start / eop) . )* {

      def content

        [:text, text_value ]

      end

    }

  end

  # Example: \tag{inner_text}

  rule tag

    tag_start tag_type "{" inner_text "}" {

      def content

        [tag_type, inner_text.content]

      end

    }

  end 

  # Example: \emph{inner_text}

  rule inner_text

    ( !'}' . )* {

      def content

        [:inner_text, text_value]

      end

    }

  end

  rule eop

    newline 2.. {

      def content

        [:newline, text_value]

      end

    }

  end

  rule tag_type

    "emph" / "texttt"

  end

  rule newline

    "\n"

  end

  rule tag_start

    "\\"

  end

end

[Clifford Heath]

Will,

I can't spot anything straight away. In a situation like this, I tend to do the following:

require 'ruby-debug'
Debugger.start
trap "INT" do
puts caller*"\n\t"
debugger
end

Run your program and hit ^C.

Clifford Heath.

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[Will Myers]

Thanks for the reply, Clifford. 

When I run this and hit ^C I usually hit one of the following three places: 

(eval):118:in `call'
(eval):118:in `_nt_text'
(eval):73:in `block in _nt_paragraph'
(eval):67:in `loop'
(eval):67:in `_nt_paragraph'

or 

(eval):206:in `call'
(eval):206:in `_nt_tag'
(eval):69:in `block in _nt_paragraph'
(eval):67:in `loop'
(eval):67:in `_nt_paragraph'

or 

(eval):68:in `call'
(eval):68:in `block in _nt_paragraph'
(eval):67:in `loop'
(eval):67:in `_nt_paragraph'

I'm afraid that doesn't clear anything up for me, I already knew where it was spinning from pry. Any other thoughts?

[Clifford Heath]

Ahh, found it. Paragraph matches an unlimited number of tags or text.
Text can however match zero-length input; so you're getting an unlimited
number of variable-length texts. Try using + instead of * in text.

Clifford Heath.

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[Will Myers]

Clifford, 

That was it! Many thanks.