From: William James <w_a_x_man@...>
Date: 2009-01-12T09:24:24+09:00
Subject: Re: functional programming

Joel VanderWerf wrote:

> 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]

mean = proc{|a| a.inject{|s,x| s+x} / a.size.to_f }
    ==>#<Proc:0x027949e0@(irb):19>
data.map &mean
    ==>[2.0, 5.5]