From: Robert Klemme <bob.news@...>
Date: 2004-08-07T18:31:23+09:00
Subject: Re: Defining a new function by composition


"Edgardo Hames" <ehames@gmail.com> schrieb im Newsbeitrag
news:478c16ae0408061345100e8692@mail.gmail.com...
> On Sat, 7 Aug 2004 04:46:25 +0900, Robert Klemme <bob.news@gmx.net> wrote:
> >
> > "Edgardo Hames" <ehames@gmail.com> schrieb im Newsbeitrag
> > news:478c16ae0408061209424c2032@mail.gmail.com...
> > >
> > > I would like to add a method to the Array class, say Array#pop! which
> > > is actually split!(-1). But then, I can think of a more general
> > > problem: define a new function by composition of two or more
> > > functions.
> >
> > How about
> >
> > class Array
> >  def pop!() split!(-1) end
> > end
>
> I imagined this. But, I thought you were going to surprise me with a
> weird (or unimagined) way to use alias ;-)

:-) Not possible because of the argument.

Here's another solution - even more functional, although I still think this
looks a bit more elegant in functional languages:

def concat3(*fun)
  lambda {|*a| fun.inject(a) {|val,f| f.call(*val)} }
end

>> foo = lambda {|x| "<#{x}>"}
=> #<Proc:0x1019fac0@(irb):17>
>> bar = lambda {|x| "[#{x}]"}
=> #<Proc:0x10194d38@(irb):18>
>> xx3 = concat3 bar, foo
=> #<Proc:0x101b7250@(irb):15>
>> xx3.call 100
=> "<[100]>"
>> xx3[ 100 ]
=> "<[100]>"

As you can see, there are plenty ways to do this.  And you can even use Ruby
as a functional language, although I'd say best use is made of it if you use
it OO.

Regards

    robert