From: Lloyd Zusman <ljz@...>
Date: 2004-04-21T22:25:43+09:00
Subject: Re: Ruby proposal: MAIN_BINDING

Szymon Drejewicz <drejewic@wsisiz.edu.pl> writes:

> What do you think about MAIN_BINDING for use it with eval():
>
>         eval("a = 'hello'",MAIN_BINDING)
>         puts a
>
> outputs:
>         hello
>
>
> ?

Well, the following does work:

  a = 'goodbye'
  eval("a = 'hello'", binding())
  puts a   # => hello

The reason has to do with the differing manner in which ruby interprets
"puts a" in the presence and absence of a previous variable definition
for "a".

If "a" is previously defined as a variable, the compiler causes the
"puts a" command to simply output its value; but if "a" is not
previously defined, my understanding is that "puts a" interprets "a" as
a method call.  In this case, "eval" statement (whose command is not, of
course, touched by the interpreter) indeed sets the "a" variable in the
global scope, but the "print" statement doesn't access it.

I'm don't know if there's a syntactical way around this.

-- 
 Lloyd Zusman
 ljz@asfast.com