From: Mike Gold <mike.gold.4433@...>
Date: 2009-02-08T23:46:02+09:00
Subject: Re: eval statement

Albert Schlef wrote:
>>Jonathan Wills wrote:
>>> 
>>> eval('a=2')
>>> puts a
>>> 
>>> r.rb:2:in `<main>': undefined local variable or method `a' for
>>> main:Object (NameError)
>Mike Gold wrote: 
>>
>> The contents of 'a=2' is not seen by the parser when the file is read, 
>> so in the second case the 'a' in 'puts a' is determined to be a method 
>> call: "call method 'a', then call method puts".
> 
> I don't think you are correct here. The string 'a=2' is first *parsed*, 
> only then evaluated.

I can't pinpoint where the misunderstanding is.  The _contents_ of 'a=2' 
is not seen by the parser when the file is read, meaning the parser just 
sees a string and nothing more.  The AST of the file would be the same 
if the string were 'foo'.  Because no local assignment syntax is 
encountered by the parser _when the file is read_, the 'a' in 'puts a' 
is determined to be a method call.

The parsing and evaluating of 'a=2' is done separately at runtime, long 
after the 'a' in 'puts a' was determined to be a method call.

> If your theory was correct, eval('whatever=567') 
> would have generated some error (because there's no 'whatever=' method).

I don't know what this theory is, but in any case 'whatever=567' would 
not under any circumstances be interpreted as calling method 
'whatever='.  The syntax x=y is always local assignment. 
(self.whatever=567 for the method call.)
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