more condenced representation

Author: rssh

shared/src/test/scala/gopher/monads/Queens.scala

@@ -16,17 +16,17 @@ class QueensSuite extends FunSuite {
   import scala.concurrent.ExecutionContext.Implicits.global
   given Gopher[Future] = SharedGopherAPI.apply[Future]()
 
-  type State = Vector[(Int,Int)]
+  type State = Vector[Int]
 
   extension(queens:State) {
 
     def isUnderAttack(i:Int, j:Int): Boolean = 
-      queens.exists{ (qi,qj) => 
+      queens.zipWithIndex.exists{ (qj,qi) => 
         qi == i || qj == j || i-j == qi-qj || i+j == qi+qj
       }
-      
-    def put(i:Int, j:Int): State =
-     queens :+ (i,j) 
+
+    def asPairs:Vector[(Int,Int)] =
+      queens.zipWithIndex.map(_.swap)
 
   }
 
@@ -38,14 +38,14 @@ class QueensSuite extends FunSuite {
       val i = state.length
       if i < N then 
         for{ j <- 0 until N  if !state.isUnderAttack(i,j) } 
-          ch.write(state.put(i,j))
+          ch.write(state appended j)
       ch.close()
     }
     ch
 
   def solutions(state: State): ReadChannel[Future,State] =
     async[[X] =>> ReadChannel[Future,X]] {
-      if(state.size < N) then
+      if(state.length < N) then
         val nextState = await(putQueen(state))
         await(solutions(nextState))
       else
@@ -57,7 +57,7 @@ class QueensSuite extends FunSuite {
      async[Future] {
        val r = solutions(Vector.empty).take(2)
        assert(!r.isEmpty)
-       println(r)
+       println(r.map(_.asPairs))
      }
   }