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See "Squinting at Power Series" and "Power Series, Power Serious".

/* 
   Please try the NoviceExamples before these examples
To compile:
   nicec --classpath "jcspclasses.jar;nice-csp.jar" --sourcepath .. -a power.jar power
To run:
   java -cp "jcspclasses.jar;power.jar" power.fun
*/

import nice.csp;
import nice.csp.util;
import jcsp.plugNplay.* (!);

let ArrayList<ProcessManager> m = new ArrayList();

void main(String[] args){  

   void stopProcesses(){
      for (each : m) each.stop;
      m.clear;   
   }

   let count = 5;
   
   println("");
   println("=== derivatives ===");    
   let d = derivative(ones());  
   print(d, count);  
   stopProcesses();
      
   println("");
   println("=== integrals ===");    
   let i = integral(ones());  
   print(i, count); 
   stopProcesses();
      
   println("");
   println("=== 1 / (1-x)**2 ==="); 
   let o = split(ones());            
   print(o[0]*o[1], count);    
}


PowerSeries ones(){ 
   void->void b(PowerSeries P){      
      void a(){
         while(true)
            P.write( RationalOne() );
      }    
      return a;    
   }
   return managedPS(b);
}


PowerSeries `*`(PowerSeries F, PowerSeries G){
   void->void b(PowerSeries P){
      void a(){
         let f = F.read;
         let g = G.read;
         let FF = split(F);
         let GG = split(G);    
         P.write(f * g);  
         let fG = f * GG[0];      
         let gF = g * FF[0];
         let xFG = xmul(FF[1] * GG[1]);      
           
         while(true)               
            P.write(fG.read + gF.read + xFG.read); 
      } 
      return a;    
   }
   return managedPS(b);
}


PowerSeries[] split(PowerSeries F){     
   let P0 = new PowerSeries(channel: 
      One2OneChannel.create(new InfiniteBuffer()));
   let P1 = new PowerSeries(channel: 
      One2OneChannel.create(new InfiniteBuffer()));        
   
   let pm = new ProcessManager( new Delta2(F.channel,P0.channel,P1.channel) );
   m.add(pm);
   pm.start;  
   return [P0,P1];
}


PowerSeries `*`(Rational c, PowerSeries F){
   void->void b(PowerSeries P){  
      void a(){ while(true) P.write(c*F.read); }
      return a;    
   }
   return managedPS(b); 
}


PowerSeries xmul(PowerSeries F){
   void->void b(PowerSeries P){     
      void a(){
         P.write(RationalZero());
         while(true) P.write(F.read);
      }    
      return a;    
   }
   return managedPS(b);    
}


void print(PowerSeries F, int n){
   void a(){
      var count = 0;
      println("Value\t\tThreads");      
      while(count<n){     
         println(F.read + "\t\t" + Thread.activeCount());
         count++;
         }
   } 
   seq(a).run;
}


PowerSeries derivative(PowerSeries F){
   void->void b(PowerSeries P){ 
      void a(){
         var f = F.read;
         var n = 1;
         while(true){
            f = F.read;      
            P.write( new Rational(num: n*f.num, den: f.den) );
            n++;
         }
      } 
      return a;    
   }
   return managedPS(b);
}


PowerSeries integral(PowerSeries F){
   void->void b(PowerSeries P){ 
      void a(){
         var f = F.read;
         var n = 1;
         while(true){
            f = F.read;      
            P.write( new Rational(num: f.num, den: f.den*n) );
            n++;
         }
      } 
      return a;    
   }
   return managedPS(b);
}


class PowerSeries {
   One2OneChannel channel = new One2OneChannel();

   Rational read() = cast(channel.read);   
   void write(Rational a) = channel.write(a);
}


PowerSeries managedPS(PowerSeries->(void->void) f){
   let P = new PowerSeries();
   let a = f(P);
   let pm = new ProcessManager( seq(a) );
   m.add(pm);
   pm.start;  
   return P;
}

/* Notes - language
Experimental use of the "Communicating Sequential Processes for Java TM (JCSP)" library.

See "Squinting at Power Series" 
   http://citeseer.nj.nec.com/mcilroy89squinting.html

and "Power Series, Power Serious"
   http://citeseer.nj.nec.com/mcilroy98power.html


   >java -cp jcspclasses.jar;power.jar power.fun

   === derivatives ===
   Value           Threads
   1               3
   2               3
   3               3
   4               3
   5               3

   === integrals ===
   Value           Threads
   1               3
   1/2             3
   1/3             3
   1/4             3
   1/5             3

   === 1 / (1-x)**2 ===
   Value           Threads
   1               7
   2               15
   3               19
   4               27
   5               27
*/

public class Rational {
   long num; // dividend
   long den; // divisor
   
   {
      let denominator = abs(den); 
      var numerator = num;
      if (den<0) numerator = -numerator;
      
      let gcd = numerator.gcd(denominator);
      if (gcd == 1){
         num = numerator;
         den = denominator;
      }
      else {
         num = numerator/gcd;
         den = denominator/gcd;
      }      
   }
      
   toString(){   
      if (den == 1) 
         return num.toString; 
      else 
         return num + "/" + den;     
   }                           
}

Rational `+`(Rational a, Rational b){
   if (a.den == b.den)
      return new Rational(num: a.num + b.num, den: a.den);
   else
      return new Rational(
         num: (a.num * b.den) + (b.num * a.den), 
         den: a.den * b.den
         );      
}   

Rational `*`(Rational a, Rational b) =
  new Rational(num: a.num * b.num, den: a.den * b.den); 
  
Rational RationalOne() = new Rational(num: 1, den: 1);
Rational RationalZero() = new Rational(num: 0, den: 1);