From: Mike Gold <mike.gold.4433@...>
Date: 2009-01-13T12:07:28+09:00
Subject: Re: functional programming

Brian Candler wrote:
> Mike Gold wrote:
>> Brian Candler wrote:
>>>
>>>Yes, a variable holding a lambda is a different beast to a method. As 
>>>you said, methods are associated with objects, and lambdas are not. 
>>>Usually one suits the usage case better than the other.
>>>
>>>I find the distinct behaviours of both to be very useful in practice.
>>
>> Can you give an example of where the difference is "very useful"?
> 
> Well, as you know, blocks are roughly just in-line lambdas:
> 
>   10.times { |x| puts x }
> 

If by "roughly" you mean "not", then yes.  Blocks are not lambdas, they 
are Procs.

> I was thinking of the following properties of the method/lambda 
> difference:
> 
> (1) You can return directly from a method, even from inside blocks.
> 
>   class Foo
>     def bar
>       10.times { |x| ...
>         10.times { |y| ...
>           return "foo" if baz(x,y)
>         }
>       }
>     end
>   end

Lambdas do not abort the enclosing method with 'return'.

def lambda_test
  func = lambda {
    return
  }
  puts "before"
  func.call
  puts "after"
end

def proc_test
  func = Proc.new {
    return
  }

  puts "before"
  func.call
  puts "after"
end

lambda_test # => before
            #    after

proc_test   # => before

The topic was about the problems arising from the syntactic difference 
between methods and lambdas.  You've changed gears to a generic 
discussion about procs.  My question is yet unaddressed: why is 
func.call() or func[] or func.() "very useful" compared to func()?  As I 
mentioned, in every case I've found it to be a hassle, for the reasons 
previously stated.
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