From: Stefan Lang <langstefan@...>
Date: 2005-02-13T09:34:58+09:00
Subject: Re: difficulty with blocks

Johannes Ahl-mann wrote:

> hi,
> 
> sorry for answering my own post, but i am adopting ruby at an incredible
> rate. i know python quite well and it took me literally mere minutes to
> get the BASIC hang of blocks... i've been programming in ruby for 3
> hours now and it already feels like home! not much cosier than python,
> but the block closures and the possibility of continuations drags me
> into ruby nonetheless ;-)
> 
> well, i've got a rather satisfactory solution to my problem and would now
> like to ask whether my implementation can be considered "the ruby way" or
> if it feels rather strange to the senior rubiists (i.e. people who have
> programmed in ruby for more than 3 hours) *ggg*
> 
> 
> ### snip ###
> 
> 
> def fib_block &block
>   a, b = 1, 1
>   while true:
>     block.call(a)
>     a, b = b, a+b
>   end
> end
> 
> require 'generator'
> def fibUpTo n, &block
>   fibs = Generator.new do |g|
>     fib_block {|val| g.yield val}
>   end
> 
>   while (f = fibs.next()) < n
>     block.call(f)
>   end
> end
> 
> def into(anArray)
>   return proc {|val| anArray << val}
> end
> fibUpTo 20, &into(a = [])
> puts a
> 

A shorter version without the generator library would be:
##################################################
#!/usr/bin/ruby

def fib
    a, b = 1, 1
    loop {
        yield a
        a, b = b, a + b
    }
end

def fibUpTo n
    fib { |val|
        break if val > n
        yield val
    }
end

a = []
fibUpTo(20) { |val| a << val }
puts a
##################################################

> 
> ### snip ###
> 
> thx and forgive me for answering my own questions. i really shouldn't do
> that ;-))
> 
> Johannes
> 
> P.S.: what is it with the implicit blocks in ruby. i am aware that many
> people seem not to be explicitely passing the block into a function, but
> i really find that distracting and too much of a perl idiom. is my way
> alright, or was it unidiomatic??
> 
> P.P.S: is there a better way to write "fib_block {|val| g.yield val}"?
> maybe something like "fib_block.apply(g.yield)" or so. i guess not, but
> the repetition bothers me!