From: Ken Bloom <kbloom@...>
Date: 2009-01-19T09:38:45+09:00
Subject: Re: Why eval is not failing in the third case ( c3)

On Sun, 18 Jan 2009 16:35:31 -0500, Raj Singh wrote:

>>> c1 = 'hello'
>>> eval c1
> NameError: undefined local variable or method `hello' for main:Object
> 
>>> c2 = 'hello #{hi}'
> => "hello \#{hi}"
>>> eval c2
> NameError: undefined local variable or method `hello' for main:Object
> 
>>> c3 = '#{hi} hello'
> => "\#{hi} hello"
>>> eval c3
> => nil
> 
> 
> My question is why the eval of c3 is returning nil. It should fail
> saying that undefined local variable just as it did in the case of c2 ?

In the second and third cases, everything after (and including) the # is 
interpreted as a comment. Thus, you're executing

hello
hello #{hi}
#{hi} hello

In case 1, hello is a undefined method, so a NameError is raised
In case 2, hello comes before the comment, so it gets executed (with no 
arguments). A NameError is raised because it's an undefined method.
In case 3, hello is part of the comment. Nothing gets executed, so no 
NameError is raised.



-- 
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/