From: Tom Cloyd <tomcloyd@...>
Date: 2009-03-25T19:52:38+09:00
Subject: Re: how to call instance method from within Treetop gem

Justin Collins wrote:
> Tom Cloyd wrote:
>> I'm trying to call an instance method from within a gem (Treetop), 
>> and nothing I've tried is working (3 hours into it - no results). 
>> I'll do my best to simplify the problem.
>>
>> I have a class instance which sets things up with this...
>>
>>    Treetop.load '../data/sn_grammar' # <= this loads a data file 
>> which will be process as Ruby, after some preprocessing
>>
>>    @parser = Base_grammarParser.new # < = Treetop class instance
>>
>> My class method with the code above then calls another method in the 
>> same class - both in my module SN, class SetNet.
>>
>> The other method then calls a method of the @parser instance, and 
>> THAT one gives to eval some of the text in the sn_grammar file 
>> referenced in the first code line above. That text then calls another 
>> method - showhelp - back in my class instance. But it cannot find it. 
>> I'm not naming it correctly, somehow.  I get this error:
>>
>> (eval):71:in `act': undefined method `showhelp' for 
>> SyntaxNode+HelpMain0 offset=0, ".h":Treetop::Runtime::SyntaxNode 
>> (NoMethodError)
>>        from ../lib/setnet/SN.rb:265:in `proc_command'
>>        from ../lib/setnet/SN.rb:182:in `user_interface'
>>        from ../lib/setnet/SN.rb:113:in `manage'
>>        from ../lib/setnet/SN.rb:38:in `startup'
>>        from ./setnet:26
>>
>> I've tried every permutation I can image, to tell eval how to find my 
>> method. No go.
>>
>> Module SN => class SetNet => instance setnet => method showhelp. <= 
>> That's what I'm trying to get to.
>>
>> How can I tell eval, executing off in the gem directory, where this 
>> method is found? That's my problem, I think. I'm run out of 
>> possibilities, so I'm failing to grasp something basic most likely.
>>
>> Any help would be appreciated.
>>
>> Tom
>>
>
> Hi Tom,
>
> You seem to be trying to call the showhelp method from within your 
> grammar. Is this correct? If so, note that the code within the grammar 
> is attached to SyntaxNodes as the grammar matches your text. So your 
> showhelp method is expected to be defined for SyntaxNodes.
That's the problem I didn't know how to address!
>
> Here is what I think your setup is:
>
> module SN
>  class SetNet
>    def other_method
>      @parser = Base_grammarParser.new
>      @parser.parse(text).eval
>    end
>
>    def showhelp
>    end
>  end
> end
>
> grammar Base_grammar
>  rule help
>    .* {
>      def eval
>        showhelp
>      end
>    }
>  end
> end
>
>
> If this is the case, you can just make eval take an argument:
>
>
> module SN
>  class SetNet
>    def other_method
>      @parser = Base_grammarParser.new
>      @parser.parse(text).eval(self)
>    end
>
>    def showhelp
>    end
>  end
> end
>
> grammar Base_grammar
>  rule help
>    .* {
>      def eval(sn)
>        sn.showhelp
>      end
>    }
>  end
> end
>
> Hope that helps some.
>
> -Justin
>
>
Justin,

I am in your debt. I didn't have much faith that I could explain my 
problem well enough, and simply enough, that I'd get a response. Your 
solution made sense to me (I'd wanted to do what your code does, but 
didn't know how). With a minor adjustment, it worked, which was a bit 
stunning. Here's the final version (a prototype only, but that'll get me 
launched):

#this - in my main class method
    Treetop.load '../data/sn_grammar'
    @parser = Base_grammarParser.new

#this in my secondary method
    if parse_tree = @parser.parse( @opt )
      parse_tree.act(self)
    else...

#this in my grammar rule
  # display main help
  rule help_main 
    '.h' {
    def act( sn )
      #puts 'help_main'
      sn.showhelp( [ '0', '0c', '0a', '0q', '0v', '0f', '0m', '0u' ] )
    end
    }
  end

#and this in my main, as suggested by Markus on the Treetop list -
class Treetop::Runtime::SyntaxNode
  #include SN
  def act
    elements.each { |e| 
    e.act(self) if e.respond_to? :act }
  end
end

Now I can write my grammar and get this thing working for me.

I much apppreciate your superior knowledge, and your generosity in 
sharing it.

t.

-- 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tom Cloyd, MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< tc@tomcloyd.com >> (email)
<< TomCloyd.com >> (website) 
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~