On Wed, 25 May 2005, Rob Kinyon wrote:

> (This post references the discussion at
> http://www.perlmonks.org/?node_id=458728, particularly dragonchild's
> response at the bottom.)
> For those who don't know, cribbage is a game where each player has
> access to 4 cards, plus a community card. Various card combinations
> score points. The one in question is when cards add up to 15. If you
> have a group of cards that add up to 15, you receive 2 points. This is
> for every group, so if you have a ten and 2 fives, you get 4 points.
> Two tens and two fives is 8 points. Face cards are worth 10 and aces
> are 1, for these purposes.
> I proposed the following:
> # Fifteens
> $score += 2 * all( 15 == [EMAIL PROTECTED] any( 0 .. 4 ) } );
> * Is this syntax legal?

I think so.

> * Does it do what I want it to do?

Definitely not.  It looks like you are thinking of junctions in terms of
arrays, instead of scalar quantum superpositions.

   any( 0 .. 4 )

This returns a scalar junction of the five values (0,1,2,3,4).
What you want is clearly all possible subsets of 0..4.  You probably
should write a coroutine to generate a lazy list of them.

   @hand{ $junction }

returns a scalar junction of the five cards in the hand.  Junctions
auto-thread through operators, including postcircumfixes.

   [+] $junction

returns $junction, since [+] $scalar == $scalar.  The individual values
auto-thread through.

   15 == $junction

This returns a junction of booleans.  Knowing the possible values of
@hand, all of them are false.

   all( $junction )

I'm not real good with nested junctions...

   2 * $junction

This returns another junction, with all elements doubled.  (still zeros)
You obviously want 2 * <junction>.elems, but I'm not sure if junctions
support that method.

   $score += $junction

Again this will make $score a junction of values.  It will not add each of
the junction values to $score.  You probably want something like
C< $score >>+=<< $junction.values > but that is another indication
that you should be using arrays instead of junctions.  And I'm not sure
about the object interface to junctions anyway.

> * Is there another way?

Assuming you write the subset coroutine above, how about

  $score +=
  ( subsets(0..4) ==> map { 2 * (15 == [+] @[EMAIL PROTECTED]) } ==> [+] )

~ John Williams

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