From: Alan Forrester <af17g11@...>
Date: 2013-01-22T05:22:24+09:00
Subject: Re: Enumerator usage

On 21 Jan 2013, at 19:20, David Richards <lists@ruby-forum.com> wrote:

> I don't understand the following:
> 
> 3.times { |i| puts(i) }  # ok
> 3.times.class  # Enumerator
> n = 3.times
> n.class  # Enumerator
> n { |i| puts(i) }  # error!?
> 
> To a new Ruby student this error seems 'conceptually wrong'.
> 
> Playing around a bit I've discovered that this works:
> 
> n.each { |i| puts(i) }
> 
> As does:
> 
> 3.times.each { |i| puts(i) }
> 
> Does this inconsistency result from a parser-level layer of 'syntactic
> sugar'? I'm also getting a sense that a 'block' is a parser-level
> construct,
> and a 'Proc' is an execution-level object.
> 
> So, a related question: given an Enumerator and a 1-ary Proc (lambda):
> 
> n = 3.times
> f = lambda { |i| puts(i) }
> 
> What expression allows us to 'map' or 'apply' the Proc to each
> enumerated value?
> 
> There just seems to be something really 'wrong' about how Ruby treats
> functions:
> 
> def f2(i)
>    puts(i)
> end
> 
> f2.class # error!?
> 
> Functions are not first-class objects? I actually have no idea what f2
> is. Clearly its not a symbol bound to an object. It's 'something else'.
> 
> Intuitively I would have expected the follow two constructs to produce
> operatively identical objects:
> 
> def f2(i)
>    puts(i)
> end
> 
> f2 = lambda { |i| puts(i) }
> 
> I'm really puzzled by this. Coming from years of programming in Scheme
> I'm quite used to dealing with syntax-layer transformations. But there
> is evidently something else going on with Ruby that violates a lot of my
> intuitions and expectations. I'm hoping that once I understand it better
> it will start to look 'elegant' and 'beautiful', but right now it looks
> kinda 'scary' and 'repugnant'.
> 
> Help please!

In Ruby objects are not first first class.

The commonly given reason for this is that non-first-class blocks are faster because you don't have to create objects to use them:

http://mudge.name/2011/01/26/passing-blocks-in-ruby-without-block.html

Alan