From: Bob Hutchison <hutch@...>
Date: 2006-01-08T23:05:22+09:00
Subject: Re: Iterator Fu Failing Me


On Jan 7, 2006, at 5:43 PM, Robert Klemme wrote:

> Bob Hutchison <hutch@recursive.ca> wrote:
>> On Jan 7, 2006, at 1:08 PM, Robert Klemme wrote:
>>>>
>>>> You mean #detect or #select?
>>>
>>> #detect - because it stops as soon as it has a hit while #select
>>> will return an array.  We need just the first hit.
>>>
>>>>> [nil,nil,nil,"w",2,3].find {|x|puts x;x}
>>> nil
>>> nil
>>> nil
>>> w
>>> => "w"
>>>>> [nil,nil,nil,"w",2,3].select {|x|puts x;x}
>>> nil
>>> nil
>>> nil
>>> w
>>> 2
>>> 3
>>> => ["w", 2, 3]
>>>
>>
>> The trouble is that detect returns the 'x' not the result of
>> processing x successfully (or, in terms of the original post, the
>> class that accepts the token not the result of the #parse? method).
>> That's why you have to capture the result in the block. Map returns
>> the result of processing.
>
> Aargh!  I shoul've tested more carefully.  Yes you're completely  
> right.  But the inject version still works, I think that's then my  
> favourite.
>
> elements = tokens.map do |tok|
>  parsers.inject(false) {|a,pars| a = pars.parse? tok and break a}
> end

Personally, I don't like the break. It'd be very nice if there were  
equivalent operations returning the result of the calculation rather  
than the object.

>
> Thanks for correcting me!

Sorry for the brutally finger-tied attempts at communication :-)

>
>    robert
>
>

----
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