From: Brian Candler <B.Candler@...>
Date: 2007-04-24T17:48:07+09:00
Subject: Re: Arrow operator with dash instead of equals (->)

On Tue, Apr 24, 2007 at 06:52:14AM +0900, Andrew Green wrote:
> Anyway, all of this is processed by our own interpreter, including, for
> example, the rule
> 
>         has_parent->place_of_birth
> 
> As you can see it's mainly declarative. However this part
> 
>         |{ (ROOT->has_given_names).textBPV + " " + (ROOT->has_last_names).textBPV }|
>         
> is read by our interpreter only as a string between a |{ and a }| .
> 
> That string is then passed to the Ruby interpreter and is meant to be
> run (from within a specific context that our interpreter determines). In
> these bits we don't want just our language running about, of course, we
> want full-blown Ruby code with extensions that allow a programmer to
> refer to the graph traversal rules using a syntax similar to that used
> in the rule definitions that appear _outside_ the Ruby code blocks.

And my suggestion still stands: if what you want to appear inside {..} is a
language which has -> as an operator, then a 'clean' (albeit heavyweight)
option is to write your own expression parser using an LALR parser
generator.

The expression parser can build a syntax tree, and then you can either walk
this tree yourself, or use it to generate Ruby code as its output, which you
can then run.

A completely different option would be to use Perl instead of Ruby, since
Perl has a -> dereference operator. But then you will have to put lots of
dollar signs and curly brackets in.

B.