From: Randy Kramer <rhkramer@...>
Date: 2007-11-09T06:39:04+09:00
Subject: Re: local variables, eval, and parsing

On Thursday 08 November 2007 01:45 pm, furtive.clown@gmail.com wrote:
> On Nov 8, 1:10 pm, Randy Kramer <rhkra...@gmail.com> wrote:
> > On Thursday 08 November 2007 11:25 am, furtive.cl...@gmail.com wrote:
> >
> > > As explained in the links I gave, the problem is due to the
> > > determination of local variables at compile time.  Really all that is
> > > needed is a way to insert code before parsing, like perl's BEGIN block.
> >
> > Ruby has a BEGIN {} (and END) block as well--have you tried that?  
(pickaxe2
> > pg. 318)
> >
> 
> BEGIN {
>    eval "foo = 99"
> }
> puts foo
> 
> => test.rb:6: undefined local variable or method `foo' for main:Object
> (NameError)

Hmm, I probably can't help you--pointing out the BEGIN block might have been 
the limits of my knowledge, but...

Are you sure the undefined local variable is a parsing problem?  Look at this:

The following gives me the (same) undefined local variable error that you get:

./test.rb:3: undefined local variable or method `foo' for main:Object 
(NameError)

#! /usr/bin/env ruby
BEGIN { foo = 99 }
puts foo

On the other hand, making it an instance variable (a little more towards the 
global range of things) makes it work just fine.

#! /usr/bin/env ruby
BEGIN { @foo = 99 }
puts @foo

I don't know why you need the eval.

Good luck!
Randy Kramer


> I realized after posting this that BEGIN wasn't the right analogy as
> it still executes too late, after parsing is already done.  Literal
> code needs to be inserted into the buffer before parsing, something
> like a C-preprocessor #include.
> 
> The original motivation was to have a config file for my Rakefile.  An
> ugly workaround is to move the content into Rakefile.main and make a
> one-liner Rakefile:
> 
> eval(File.open("Rakefile.config") { |f|
>         f.read
>      } + "\n" +
>      File.open("Rakefile.main") { |f|
>         f.read
>      })