From: "Jean-François Trân" <jftran@...>
Date: 2008-10-22T01:12:38+09:00
Subject: Re: Ruby way to take some action only once in a loop?

2008/10/21 Evgeniy Dolzhenko <dolzenko@gmail.com>:

> The most embarrassing fact about Nobu's solution is its all in Pickaxe
> http://www.rubycentral.com/pickaxe/tut_expressions.html :)
>
> Exactly what happens is described in this quote: "You can use a Ruby range
> as a boolean expression. A range such as exp1..exp2 will evaluate
> as false until exp1 becomes true. The range will then evaluate
> as true until exp2 becomes true. Once this happens, the range resets,
> ready to fire again".
>
> So exp1 (first=true) evaluates to true, then interpreter evaluates
> boolean range
> to true and waits until exp2 (false) becomes true which will never happen,
> but on all consequent runs "and first" will guard "if" body from executing

thanks for the explanations.

> (because exp1 is not executed anymore "first" gives you nil,
> AFAIK what happens here is that "first" becomes "defined" name for the
> interpreter
> after first assignment but I can't say I have good grasp on this
> "scoping" feature).

I guess it can be explained because at parse time, Ruby has seen
first assignment in the condition, and then considered 'first' as a variable
even if the assignment is not executed.

it's also in the Pickaxe :)

http://www.rubycentral.com/pickaxe/language.html
chapter : Variable/Method Ambiguity

   -- Jean-François.

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