From: Brian Candler <B.Candler@...>
Date: 2003-07-07T20:11:38+09:00
Subject: Re: trapping compile time errors -- alas

On Mon, Jul 07, 2003 at 07:36:42PM +0900, Gerard A.W. Vreeswijk wrote:
> On Mon, 7 Jul 2003 18:38:03 +0900, Brian Candler <B.Candler@pobox.com>
> wrote:
> 
> >No, there cannot be such a solution.
> >
> >Ruby runs programs by
> >(1) parsing the code, and converting to an Annotated Syntax Tree
> >(2) running the AST
> >
> >If step 1 fails, no code will run at all.
> >
> >Brian.
> >
> 
> I am convinced.  So Ruby BEGIN differs from Perl BEGIN.  Alas I'd say:

I'd say Ruby's model is much cleaner. It's very clear which is the parsing
stage, and which is the execution stage - and personally I wouldn't want
Ruby to attempt to execute any program which it could not even parse!

Note that things like 'require' and class definitions don't actually happen
until the execution stage either:

  class Foo
    def wibble
    end
  end           # << class Foo does not exist until this point has been RUN
  a = Foo.new

This means you can do conditional creation of classes:

  if ARGV[0] == "test"
    class Foo
      def wibble
        puts "Testing only"
      end
    end
  else
    class Foo
      def wibble
        puts "Live environment"
      end
    end
  end
  Foo.new.wibble

$ ruby x.rb
Live environment
$ ruby x.rb test
Testing only

Regards,

Brian.