We can apply some complex constraint expressions directly to the
score. However, a more general notion is to encapsulate a
constraint expression into a compositional rule (implemented by a
procedure) which then can be applied one or more times.

Example: choral melody with simple voice leading rule. Example
introduces the notion of a context: a voice leading rule makes a note
and its previous note interdependend.


declare
local
   MIDI pitch domain reduction: only 'wite keys' (c major)
   proc {InCMajor MyNote}
      {List.forAll [1 3 6 8 10]	list of 'black' pitch classes (c=0)
       proc {$ BlackKey}
	  {FD.modI {MyNote getPitch($)} 12} \=: BlackKey
       end}
   end
   Determine the pitch of the first and last note of MyVoice
   proc {StartAndEndWithFundamental MyVoice}
      Notes = {MyVoice getItems($)}
   in
      {Notes.1 getPitch($)} = 60
      {{List.last Notes} getPitch($)} = 60
   end   
   voice leading: only intervals up to a fifth, no pitch repetition
   proc {NoBigJump Pitch1 Pitch2}
	 all intervals between minor second and fourth are allowed
	 {FD.distance Pitch1 Pitch2 '>=:' 1}
	 {FD.distance Pitch1 Pitch2 '=<:' 5}
   end
in
   proc {ChoralMelody MyMelody}
      N = 9
   in
      MyMelody = {Score.makeScore
		  seq(items: {LUtils.collectN N
			      fun {$}
				 predetermined and constant note durations
				 note(duration: 4
				       pitch: {FD.int 53#72}
				       amplitude: 80)
			      end}
		      startTime: 0
		      timeUnit:beats(4))
		  unit}
      
      Apply compositional rules:
      
      rule on melody
      {StartAndEndWithFundamental MyMelody}
      rule on single notes 
      {MyMelody forAll(test: isNote InCMajor)}
      rule on pitch pair
      {Pattern.for2Neighbours {MyMelody mapItems($ getPitch)}
       NoBigJump}
   end
end

SDistro.exploreOne simplifies definition of a CSP with a score a solution: the score distribution strategy is not part of the script but given to SDistro.exploreOne.
{SDistro.exploreOne ChoralMelody
 unit(order:size value:random)}

{OS.srand 11}			the random seed can be set to 'select' a solution