/* 

  Qualitative reasoning in Picat.

  This is a port of the Prolog code of qualitative reasong 
  from Bratko "Prolog programming for Artificial Intelligence" 
  (4th edition), page 528f.
  

  This Picat model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/

main => go.

go ?=>
  circuit1(SwitchPos,BulbStat,Lightness),
  println([switchPos=SwitchPos,bulbStat=BulbStat,lightness=Lightness]),
  fail,
  nl.

go => true.

go2 ?=>
  circuit2(Sw1, Sw2, Sw3, B1, B2, B3, L1, L2, L3),
  println([sw1=Sw1, sw2=Sw2, sw3=Sw3, b1=B1, b2=B2, b3=B3, l1=L1, l2=L2, l3=L3]),
  fail,
  nl.

go2 => true.

go3 => 
  % page 529
  circuit2(on, on, on, ok, ok, ok, L1, L2, L3),
  println([l1=L1, l2=L2, l3=L3]),
  fail,
  nl.
go3 => true.

go4 => 
  % page 529
  circuit2(_, _, off, B1, B2, B3, light, _, dark),
  println([b1=B1, b2=B2, b3=B3]),
  fail,
  nl.
go4 => true.


go5 => 
  % page 530
  circuit2(SwPos1, SwPos2, SwPos3, ok, ok, ok, _, _, light),
  println([swPos1=SwPos1,swPos2=SwPos2,swPos3=SwPos3]),
  fail,
  nl.
go5 => true.



%  Modelling simple electric circuits
%  Qualitative values of voltages and currents are: neg, zero, pos

%  Definition of switch
%  switch( SwitchPosition, Voltage, Current)

% Note: we cannot use index/3 here since all variables
% are not bound.
% Switch on: zero voltage
switch( Pos, Voltage, _Current) ?=> Pos=on, Voltage=zero.

% Switch off: zero current
switch( Pos, _Voltage, Current) => Pos=off, Current=zero.

%  Definition of bulb
%  bulb( BulbState, Lightness, Voltage, Current)
bulb( BulbState, Lightness, _Voltage, Current) ?=> 
   BulbState=blown, Lightness=dark, Current=zero.
bulb( BulbState, Lightness, Voltage, Current) ?=>
  BulbState=ok, Lightness=light, Voltage=pos,Current=pos.
bulb( BulbState, Lightness, Voltage, Current) ?=>
  BulbState=ok, Lightness=light, Voltage=neg,Current=neg.
bulb( BulbState, Lightness, Voltage, Current) ?=>
  BulbState=ok, Lightness=dark, Voltage=zero,Current=zero.

%  A simple circuit consisting of a bulb, switch and battery
circuit1( SwitchPos, BulbState, Lightness)  =>
   println($circuit1( SwitchPos, BulbState, Lightness)),
   switch( SwitchPos, SwVolt, Curr),
   writeln(after1=SwitchPos),
   bulb( BulbState, Lightness, BulbVolt, Curr),
   qsum( SwVolt, BulbVolt, pos).     % Battery voltage = pos

%  A more interesting circuit made of a battery, three bulbs and 
%  three switches

circuit2( Sw1, Sw2, Sw3, B1, B2, B3, L1, L2, L3)  =>
   switch( Sw1, VSw1, C1),
   bulb( B1, L1, VB1, C1),
   switch( Sw2, VSw2, C2),
   bulb( B2, L2, VB2, C2),
   qsum( VSw2, VB2, V3),
   switch( Sw3, V3, CSw3),
   bulb( B3, L3, V3, CB3),
   qsum( VSw1, VB1, V1),
   qsum( V1, V3, pos),
   qsum( CSw3, CB3, C3),
   qsum( C2, C3, C1).   
   
%  qsum( Q1, Q2, Q3):
%    Q3 = Q1 + Q2, qualitative sum over domain [pos,zero,neg]

index(-,-,-)
qsum( pos, pos, pos).
qsum( pos, zero, pos).
qsum( pos, neg, pos).
qsum( pos, neg, zero).
qsum( pos, neg, neg).
qsum( zero, pos, pos).
qsum( zero, zero, zero).
qsum( zero, neg, neg).
qsum( neg, pos, pos).
qsum( neg, pos, zero).
qsum( neg, pos, neg). 
qsum( neg, zero, neg).
qsum( neg, neg, neg).