From: Ryan Davis <ryand-ruby@...>
Date: 2010-02-19T06:30:25+09:00
Subject: Re: Ruby conditionals subtlety?


On Feb 18, 2010, at 11:49 , Farhad Farzaneh wrote:

> Hi,
> 
> Anyone know why thse two forms of "unless" behave differently?
> 
>> irb
> irb(main):001:0> foo = true unless defined?(foo)
> => nil
> irb(main):002:0> unless defined?(fooo) ; fooo = true ; end
> => true

oddity in the way the code is parsed:

% echo "foo = true unless defined?(foo)" | parse_tree_show 
s(:if, s(:defined, s(:lvar, :foo)), nil, s(:lasgn, :foo, s(:true)))

% echo "unless defined?(fooo) ; fooo = true ; end" | parse_tree_show 
s(:if, s(:defined, s(:call, nil, :fooo, s(:arglist))), nil, s(:lasgn, :fooo, s(:true)))