From: Ralph Mason <ralph.mason@...>
Date: 2001-11-30T08:05:54+09:00
Subject: [ruby-talk:26993] Re: first class functions in Ruby

irb(main):010:0> def sq(x)
irb(main):011:1> x+x
irb(main):012:1> end
nil
irb(main):013:0> def aMes(f)
irb(main):014:1> send(f,42) + send(f,27)
irb(main):015:1> end
nil
irb(main):016:0> aMes :sq
138
irb(main):017:0>


Like that?

----- Original Message -----
From: "MikkelFJ" <mikkelj-anti-spam@post1.dknet.dk>
Newsgroups: comp.lang.ruby
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>; <undisclosed-recipients:>
Sent: Friday, November 30, 2001 11:15 AM
Subject: [ruby-talk:26976] first class functions in Ruby


> In the thread on language design, I mentioned a wish for functions as
first
> class values.
>
> I hope someone knowing Ruby deeper than I will follow up on this.
>
> I'd like to be able to write a function that I can pass as argument to a
> Ruby message or to another function. A function is a new concept in Ruby
> context.
>
> There is a difference between messages and functions. The difference being
> that messages has a receiver (the object the member function is a member
> of).
> A function is a pure mathematical abstraction that does not have any
> implicit state like a receiver.
>
> First a way to simulate a function, then a less combersome syntax
>
> <snip>
> class DoubleFunction
>   def evaluate arg
>     arg + arg
>   end
> end
>
> #example of use
>
> def aMessage f
>   f.evaluate(42) + f.evaluate(27)
> end
>
> def main
>   aMessage MyFunction.new
> end
> </snip>
>
> improved syntax:
>
> <snip>
> fun squareFunction arg
>   arg + arg
> end
> def aMessage f
>   f(42) + f(27)
> end
> def main
>   aMessage squareFunction
> end
> </snip>
>
> "fun" is a new keyword that defines a function that is a receiverless
> message. It can be treated like any other object.
>
> It would also be nice to be able to pass a message ("def") around as a
> value. It may also make the "fun" keyword superflous. An example would be
as
> above, except that a) "fun" is replaced by "def", b) the object instance
the
> "def" is available and can by modified by the method the usual way:
>
> <snip>
> def squareFunction arg
>   arg + arg
> end
> def accumulate arg
>   if @count
>     @count = @count + arg
>   else
>     @count = arg
>   end
> end
> class Processor
>   def initilize n
>     @weight = n
>   end
>   def process f
>     f(weight)
>   end
> end
> def main
>   p = Process.new(4)
>   p.process(squareFunction)
>   p.process(accumulate)
>   aMessage squareFunction
> end
> </snip>
>
> The above example does not use the "fun" function, instead it uses two
> messages ("def"), in which one of the messages uses its ownership context,
> the other basically behaves like a function.
> Notice that the Process class is a bit tedious to write. It is a class
with
> a single function. The last example repeated with a function with partial
> evaluation instead of a Process class. The "fun" keyword has been
> reintroduced:
>
> <snip>
> fun squareFunction arg
>   arg + arg
> end
> def accumulate arg
>   if @count
>     @count = @count + arg
>   else
>     @count = arg
>   end
> end
> fun process weight f
>     f(weight)
> end
>
> def main
>   p4 = process(4)
>   p4(squareFunction)
>   process(4, squareFunction) # same as above
>   p4(accumulate)
>   aMessage squareFunction
> end
> </snip>
>
> In the above example, "p4" is a partial evaluation of the process
function.
> What happens is that the applied parameter 4 is saved in an internal
> "weight" variable, and a new function is  created with one parameter less.
> This is pretty much standard in functional programming, but it should be
> pretty straightforward to integrate in the ruby enviroment. In ML this can
> be pretty heavy stuff to implement, but due to Ruby's dynamic nature, it
> should be easy, and equally powerful.
> Microsoft added the concept of delegates to java, dubbing it J++ and
spawned
> a major lawsuit from Sun. But the concept was great and made it much
easier
> to create eventhandlers.
>
>
> MikkelFJ
>
>
>
>
>
>