From: Simon Strandgaard <neoneye@...>
Date: 2004-04-27T17:48:19+09:00
Subject: Re: Semantics of Multiple Values

Dan Doel <djd15@po.cwru.edu> wrote:
[snip] 
> The other proposition here is pattern matching, which is also in existing
> programming languages. Haskell has pattern matching. For example,
> lists can be built like so:
> 
> a : list
> 
> Where a is an element, list is a list, and ':' is the cons operator. However
> when writing list processing routines, you don't need to take a list and
> call head and such. What you can do is:
> 
> f (x:xs) = ...
> 
> And because of Haskell's pattern matching, if you pass something that is a
> cons of an item and a list, the item gets assigned to x, and the rest of the
> list gets assigned to xs. You can also do more complicated things where you
> assign the whole list to a variable, but still assign heads and tails to other
> variables and so on.  I don't know if Matz would want to take the time to
> implement such functionality, but it can be done.
> 

Ruby's case statement can do pattern matching.. relatively close to SML, Haskell.

server> ruby a.rb
result=61
server> ruby a.rb
result=61
server> expand -t2 a.rb 
def ackerman(m, n)
  case
  when m==0: n+1
  when n==0: ackerman(m-1, 1)
  else ackerman(m-1, ackerman(m, n-1))
  end
end
result = ackerman(3, 3)
puts "result=#{result}"
server>

--
Simon Strandgaard