From: Morton Goldberg <m_goldberg@...>
Date: 2007-10-11T11:27:04+09:00
Subject: Re: |how do you know when to put a variable between pipes?|

On Oct 10, 2007, at 9:35 PM, A Love of Surf wrote:

> Hi i am at about page fifty in the pickaxe book, and i have a
> question.  I see a lot of examples of a block that starts with |
> SomeVar| and I dont really understand how you know when you can do
> this or what the value will be that is passed to the variable.  What
> is the name of  this construct or the var that goes in pipes?  Thank
> you :)

In the PDF version of Pickaxe, this is explained beginning on p. 47  
(p.50 in the printed text). Read the explanation that goes along with  
the fib_up_to example. More info can be found in Chapter 22 under the  
heading: Blocks, Closures, and Proc Objects.

A quick and dirty explanation is the the vertical bars at the  
beginning of a block delimit the block's formal arguments. When the  
block is evaluated by a yield expression, the actually arguments  
passed to the yield will be assigned to the formal arguments in a  
manner similar to a function call. Just as you can't call a function  
without knowing what arguments it takes, you must know what arguments  
a method accepting a block passes to the block in order to write a  
block for that method. It is a matter of documentation.

Regards, Morton