From: Joel VanderWerf <vjoel@...>
Date: 2007-04-06T14:39:51+09:00
Subject: Re: about functional programming

gaoxtwarrior wrote:
> when it comes the method needs two block to accomplish a task,how the ruby 
> do which? for example , the classical sum(filter,mapping,iterator)(I have 
> forgotten the style, maybe,the one can search it in SICP) 

If the two blocks are applied sequentially, as part of two separate 
iterations, it's straightforward:

[1,2,"fred","wilma",5,6].select{|x|x.kind_of?(Numeric)}.inject{|s,x|s+x}
=> 14

In this special case, we can use #grep because testing for 
x.kind_of?(Numeric) is the same as testing Numeric === x (which is what 
grep(Numeric) does):

[1,2,"fred","wilma",5,6].grep(Numeric).inject{|s,x|s+x}
=> 14

More generally, though, the only way to pass more than one block to a 
method is to turn all but one of the blocks into procs, like this:

meth_with_two_blocks(proc {...}) { ... }

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407