N-Queens in FORTH

Example N-Queens for 8x8 board in FORTH for Prime FORTH

nqueens.fth

@@ -0,0 +1,48 @@
+8 constant rr
+variable ii
+variable ss
+variable xx
+variable yy
+create aa rr 1 + allot
+: rclaa @ aa + @ ;
+: stoaa @ aa + ! ;
+
+: NQPRINT
+   1 II !
+   BEGIN
+     II RCLAA .
+     1 II +!
+   II @ XX @ 1 + = until
+;
+
+ : NQCORE
+   0 SS !
+   0 XX !
+   BEGIN
+     1 XX +!
+     RR XX STOAA
+     BEGIN
+       1 SS +!
+       XX @ YY !
+       BEGIN YY @ DUP II ! 1 > IF
+         -1 YY +!
+         XX RCLAA YY RCLAA - DUP
+         0 = SWAP ABS XX @ YY @ - = OR IF
+           0 YY !
+           BEGIN XX RCLAA 1 - DUP XX STOAA DUP 0 = IF
+               -1 XX +!
+             then
+             0 <>
+           UNTIL
+         THEN
+         THEN
+         II @ 2 <
+       UNTIL
+     YY @ 1 = UNTIL
+   RR XX @ = UNTIL
+ ;
+
+: NQUEENS
+  NQCORE
+  NQPRINT
+;