From: Brian Candler <b.candler@...>
Date: 2009-12-05T01:42:04+09:00
Subject: Re: ruby language parser in ruby

Caleb Clausen wrote:
> On 12/4/09, Brian Candler <b.candler@pobox.com> wrote:
>> A minor problem with the redparse gem is that it gives most of the files
>> root-only permissions. I just did 'sudo gem install redparse'
> 
> Yes, that is indeed most unfortunate and due to be fixed in the next
> release, which is coming Real Soon Now. I'm not sure how those
> permissions got all weird (again); it's not something I usually give a
> lot of thought or attention to, I'm afraid. (Frankly, I wish rubygems
> would have warned me when I created the gem that some of the files
> were not world-readable.)
> 
>> Looking at this code - I don't think I would dare hack it. I think
>> ruby_parser is more what I was looking for.
> 
> Would you care to elaborate on that? What didn't you like and/or find
> hard to understand?

Well, all of it really.

I presume that lib/redparse.rb is the "real" parser (I also found 
lib/redparse/babyparser.rb and babynodes.rb)

It's a monolithic file, and it was hard even to see where the grammar 
began. I believe it's here:

    [
    -[UNOP, Expr, lower_op]>>UnOpNode,
    -[DEFOP, ParenedNode]>>UnOpNode,
    -[Op(/^(?:unary|lhs|rhs)\*$/), ValueNode, lower_op]>>UnaryStarNode,
    ... etc

and an example of a larger rule is like this:

   -[NumberToken&-{:negative=>true}, Op('**').la]>>
      stack_monkey("fix_neg_exp",2,Op("-@",true)){|stack|
        #neg_op.unary=true
        num=stack[-2]
        op=OperatorToken.new("-@",num.offset)
#        op.startline=num.startline
        stack[-2,0]=op
        num.ident.sub!(/\A-/,'')
        num.offset+=1
      },

I have no idea how to (a) understand, or (b) modify that. I can see 
there is quite a lot of Ruby operator abuse going on, but without 
defined semantics.

At least with racc, it's extremely well documented, in the sense that I 
have a printout of the yacc manual to refer to.

So no doubt RedParse is a fine ruby parser, and generates a fine object 
tree as its output. But it's not so good for me as a starting point for 
building languages which inherit some of ruby flavour, but are 
significantly different.
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