Fibonacci with ranges

[Russel Winder]

On Sat, 2011-03-12 at 02:15 -0800, Ali Çehreli wrote:
[ . . . ]
> void main()
> {
>      long[] data = [ 0, 1, 1, 2, 3, 5, 8 ];
> 
>      foreach (n; 0 .. data.length) {
>          assert(equal(declarative(n), data[0..n]));
>      }
> }

In fact the driver is:

unittest {
  immutable data = [
    [ 0 , 0 ] ,
    [ 1 , 1 ] ,
    [ 2 , 1 ] ,
    [ 3 , 2 ] ,
    [ 4 , 3 ] ,
    [ 5 , 5 ] ,
    [ 6 , 8 ] ,
    [ 7 , 13 ] ,
    [ 8 , 21 ] ,
    [ 9 , 34 ] ,
    [ 10 , 55 ] ,
    [ 11 , 89 ] ,
    [ 12 , 144 ] ,
    [ 13 , 233 ] ,
  ] ;
  foreach ( item ; data ) {
    assert ( iterative ( item[0] ) == item[1] ) ;
  }
  foreach ( item ; data ) {
    assert ( declarative ( item[0] ) == item[1] ) ;
  }
}

so I need to index the take-n list to return the last value.

This of course brings up the question of the signature of any factorial
function.  Without a real use case it is a rhetorical question.  What is
nice though is that there could be a neat way of generating a memoized,
i.e. cached, lazy list.

-- 
Russel.
=============================================================================
Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder at ekiga.net
41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel at russel.org.uk
London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder
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