From: Saynatkari <ruby-ml@...>
Date: 2005-04-26T12:08:07+09:00
Subject: Re: Announcing Reg 0.4.0


Le 26/4/2005, "vikkous" <google@inforadical.net> a �crit:
>itsme213 said:
>> - have you thought about the connection to duck typing?
>
>Christian Neukirchen said:
>> How does it compare to the ML style of argument matching, btw?
>
>I think you're both talking about the same thing here; the ability to
>dispatch to different methods depending on the types of method
>parameters other than just the receiver. I have thought a good deal
>about this, in fact, but not exactly in the context of Reg.

I am not certain how flexible your framework is, but as a sidenote
the typical pattern matching (term used earlier) in functional
languages is well represented by things like this:

length []      = 0             -- Matches an empty list
length (x:xs)  = 1 + length xs -- Matches&splits nonempty lists

length [1,2,3]                 -- returns 3
                               -- [1,2,3] -> [2,3] -> [3] -> []

Sorry. I just like writing Haskell :)

>The best way to do this means extending the syntax, but here's a quick
>and dirty way reg might be used to do it:
>
>#warning! won't work yet; no substitutions in reg yet
>module Scoundrels
>  def Scoundrels::bill(*args) #dispatcher for all the bills
>    send +[
>      -[Lockpick]>>:bill_the_picklock |
>      -[FakePassport,Cash,ShoePhone]>>:bill_the_spy |
>      -[Gun.reg+1, Knife]>>:bill_the_murderer |
>
>-[Laptop,Oscilloscope.reg|CellPhone|Password.reg*5]>>:bill_the_hacker
>     ].match(args.dup).first, args
>  end
>
>  #definitions of the various bills omitted
>end
>
>Then you could do:
>  Scoundrel.bill(LockPick.new)  #invokes bill_the_picklock
>  Scoundrel.bill(Laptop.new, CellPhone.new)   #invokes bill_the_hacker
>
>Maybe this could be made easier. The syntax takes a little getting used
>to, let us say.
>
>This is great; people are coming up with angles I never thought of.

E

--
template<typename duck>
void quack(duck& d) { d.quack(); }