From: "Imobach González Sosa" <imobachgs@...>
Date: 2011-01-13T14:13:56+09:00
Subject: Re: Deferring proc bindings

2011/1/12 Robert Klemme <shortcutter@googlemail.com>:
> 2011/1/12 Imobach González Sosa <imobachgs@gmail.com>:

Hi Robert,

> More precisely, it's taken from the scope where the lambda is created.
>  This does not make a difference in your example but consider this:
>
> def create
>  user = "Mr. X"
>  lambda { |arg1| puts arg1; puts user }
> end
>
> user = "Mrs. Smith"
> my_proc = create

Ok.

>> So, my question is: how could I do that 'user' was deferred until proc
>> is called?
>>
>>  def call_my_proc(&some_proc)
>>    user = 'me'
>>    some_proc.call("Hi, it's")
>>  end
>>
>>  my_proc = lambda { |arg1| puts arg1; puts user }
>>  call_my_proc(&my_proc) # "Hi, it's me"
>
> This won't work - ever.  The reason is that the binding the proc uses
> is outside of the method.  It will never see the local variable "user"
> defined inside the method body.

Right.

>> I think I could do using eval with a string, but I'd like to solve in
>> block-like form.
>
> Well you could but then again: what's the point?  What problem are you
> trying to solve?  If the binding needs to be flexible then it really
> is a case for a proc parameter.  You would need to do the assignment
> *somewhere* anyway so why not just pass the value as parameter and be
> done?  The closure is really more useful for preserving state from the
> point in time when the proc was created:
>
> def curry(*a, f)
>  lambda {|*x| f[*a.concat(x)]}
> end
>
> irb(main):004:0> plus = lambda {|a,b| a + b}
> => #<Proc:0x10039930@(irb):4 (lambda)>
> irb(main):005:0> plus2 = curry 2, plus
> => #<Proc:0x100371e4@(irb):2 (lambda)>
> irb(main):006:0> puts plus2[100]
> 102
> => nil
> irb(main):007:0>
>
> What problem are you really trying to solve?  It seems you may attempt
> to use the wrong hammer. ;-)

Yeah, you're right. Sure I'm using the wrong approach :) Indeed, I
think I've found my way through a totally different approach.

> Kind regards

Thank you for your instructive response! :)

-- 
Imobach González Sosa
imobachgs at gmail dot com