From: Logan Capaldo <logancapaldo@...>
Date: 2006-09-13T08:34:41+09:00
Subject: Re: Newbie Question: - Parse my commands...

On Wed, Sep 13, 2006 at 08:10:35AM +0900, Vidar Hokstad wrote:
> 
> paytonrules wrote:
> 
> > The first step, which I'm doing now, is to take our executable program
> > and break the parsing engine into a DLL.  That's easy.  I can then
> > create a quick ruby program so I could do this:
> >
> > irb
> > load 'rubyProg'
> >
> > parse ObjectName.Make(param1, param2, param3, param4)
> >
> >
> > The rubyProg could work this way - but I'm pretty sure I can go one
> > step farther with ruby and just type:
> >
> > ObjectName.Make(param1, param2, param3, param4)
> >
> > through ruby extensions.  The question is - how do I have the
> > interpreter pass on any code to the parser ruby can't handle it?
> 
> method_missing() can be used for this to some extent. It depends on how
> exact you want the syntax. If you can get away with changing the object
> names so that they start with a lowercase letter it's cleaner. In Ruby,
> a capital first letter of a name indicates a constant, which means you
> need some extra uglyness to handle that.
> 
> With a lowercase first letter in your object names you can do:
> 
> class MissingProxy
>   def initialize ob
>     @ob = ob
>   end
> 
>   def method_missing(sym,*args)
>     # Call your script processor here.
>     puts "PROCESS: #{@ob.to_s}.#{sym.to_s}(#{args.join(',')})"
>   end
> end
> 
> def method_missing(sym,*args)
>   MissingProxy.new(sym)
> end
> 
> myObject.Make('test',123)
> 
> 
> If, on the other hand you don't want to rewrite anything, you can wrap
> the statements like this:
> 
> begin
>   MyObject.Make('test',123)
> rescue NameError => n
>   eval("#{n.name} = MissingProxy.new(:#{n.name})")
>   retry
> end
To handle the MyObject case, you needs simply define const_missing
instead of method_missing, no need to rescue name error.
> 
> I'd consider both of these methods fairly ugly. They make trapping
> errors in your Ruby code tricky, as any misspelled object/class names
> will trigger your script interpreter instead of giving an error, but it
> does give a lot of flexibility.
> 
Agreed.