From: David Richards <lists@...>
Date: 2013-01-22T04:20:57+09:00
Subject: Enumerator usage

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!

- Dave

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