From: Gary Wright <gwtmp01@...>
Date: 2011-09-14T12:07:40+09:00
Subject: Re: Need help regarding conditionals on while loops.


On Sep 13, 2011, at 10:49 PM, Kane Williams wrote:
> They never really explained how this works though:
> 
>> while output

The while loop body is executed if the expression evaluates to a true-ish value.
In this case the expression is simply the local variable 'output'.

In Ruby all values are considered true *except* for nil and false.  In particular
0 is considered true as is an empty string, empty array, and empty hash ("", [], {}).
This often trips up Ruby newcomers.

So in your example

> def doUntilFalse firstInput, someProc
>  input  = firstInput
>  output = firstInput
> 
>  while output
>    input  = output
>    output = someProc.call input
>  end
> 
>  input
> end

the while loop will continue iterating until someProc returns a false-ish value
(either nil or false). The output of someProc is reused as its input for the
next iteration.

Gary Wright