From: David Unric <dunric29a@...>
Date: 2010-11-10T10:50:48+09:00
Subject: Re: Analyzer for errors in code ?

Ryan Davis wrote in post #960436:
>
> In python, 'mymsg' _has_ to be a variable. This isn't true in ruby. It
> can be a variable OR a method call. In the case of the latter, we don't
> know if it is valid or not without evaluating.
>
> in ruby, 'def x; mymsg; end' (the most boiled down version of your
> example) looks like this internally:
>
> % echo 'def x; mymsg; end' | parse_tree_show
> s(:defn,
>  :x,
>  s(:args),
>  s(:scope, s(:block, s(:call, nil, :mymsg, s(:arglist)))))
>
> Ruby parsed the code and decided that mymsg must be a method call. It is
> determined at runtime (since everything is late bound) who (if anyone)
> implemented the method and if not, it goes to method_missing.
>
> Python simply doesn't have this flexibility. 'x' is a variable and 'x()'
> is a call. AFAIK, there is no "__" hook equivalent to method_missing in
> python... But it has been a while for me.

Great info Ryan, thank you.

My appologies I did not realized sooner the deeper conceptual 
differencies between these languages.
Despite of that, if Ruby cann't decide if mymsg is a variable or a 
method call in advance, how does it rule out the possibility for a 
static parser to notify the 'mymsg' symbol has no assignment or method 
definiton in the source code ? I.e. if 'x' in your example is a method 
call, how can arise without some form of an assignment ?

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