From: Cleasai Beag <mick.macamhlaoibh@...>
Date: 2007-08-15T09:09:47+09:00
Subject: Re: Can a lambda or Proc object yield a value to a block?

Logan Capaldo wrote:
> You actually can use yield in a block, you just need to realize it's the
> yield of the enclosing scope:
> 
> def example
>   a_proc = lambda { yield "Hi" }
> 
>   if block_given?
>     a_proc.call
>   end
> end
> 
> example { |x| puts x }

Thanks for the reply Logan. Obviously I'll have to study Ruby's scope 
rules a bit more. I notice that I can't modify your example as follows 
to pass in a lambda object because I get the "LocalJumpError: no block 
given" error again.

a_proc = lambda { yield "Hi" }

def example2(proc)

  if block_given?
    proc.call
  end
end

example2(a_proc) { |x| puts x }

Presumably the enclosing scope for the lambda object in my example is 
outside the scope of the example2 method. It's scope is the scope in 
which it was defined which is "nowhere" really i.e. it's outside a 
class, module and method.
Presumably because of this it just can't yield a value. Does this sound 
plausible at all?

P.S. What I'm really trying to do is emulate some of things that I've 
done before in Scheme.

For example a generic "each" maker which doesn't work 'cos of the whole 
LocalJumpError thing.

def makeEach(nextValue, start, stop)
  lambda do
    x = start
    while x <= stop
      yield x
      x = nextValue.call(x)
    end
  end
end

from11to20 = makeEach(lambda {|x| x+1}, 11, 20)

from11to20 {|x| puts x*x}
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