From: Joel VanderWerf <vjoel@...>
Date: 2009-01-12T08:32:49+09:00
Subject: Re: functional programming

Mike Gold wrote:
> Brian Candler wrote:
>> (2) to understand Mike's assertion 
>> that Ruby lambdas are not first-class functions (i.e. "The difference 
>> between lambda { } and a real first-class function is quite profound").
> 
> Ruby:
> 
>   mean = lambda { |*args|
>     (args.inject(0) { |acc, x| acc + x })/args.size.to_f
>   }
>   data = [[1,2,3], [4,5,6,7]]
> 
>   data.map(&mean) # fail
>   data.map(&:mean) # fail
>   data.map { |*numbers| mean.call(*numbers) } # fail
>   data.map { |numbers| mean.call(*numbers) } # phew, found it
> 
> Haskell:
> 
>   map mean data
> 
> On this example alone, I think my characterization of "quite profound" 
> is justified.

Why isn't this the ruby candidate for comparison:

mean = lambda { |ary|
   (ary.inject { |acc, x| acc + x })/ary.size.to_f
}
data.map(&mean) # => [2.0, 5.5]

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407