From: Gennady <gfb@...>
Date: 2004-01-13T09:03:52+09:00
Subject: Re: Getting the tail of a list?

Carsten Eckelmann wrote:
> Hi everybody,
> 
> I have spent the night reading about the wonders of Scheme at 
> http://www.teach-scheme.org and have stumbled over a small demo program.
> 
> This function checks whether a guest is on the guest list or not:
> 
> (define (guest name list)
>  (cond
>    ((empty? list) 'no)
>    ((equal? name (first list)) 'yes)
>    (else (guest name (rest list)) )))
> 
> I am in love with Ruby and I'm not about to switch to Scheme, so I 
> wanted to write this in ruby:
> 
> def guest (name, list)
>  if list.empty?
>    :no
>  elseif name == list.first
>    :yes
>  else
>    guest(name, list.rest)

No Array#rest as you noted bellow, you may use list[1..-1] here.

>  end
> end

However, why not just this:

def guest(name,list)
   list.include?(name) ? :yes : :no
end

And what's wrong with boolean return values?

> 
> Well looks nice but there's a little something missing: there's no such 
> method "rest" for an array! Whereas there are things like Array#first 
> and Array#last, this seems to have been forgotten. Of course I could 
> write it like this:
> 
> def guest(name list)
>  if list.empty?
>    :no
>  elsif name == list.shift
>    :yes
>  else
>    guest(name,list)
>  end
> end
>