import CLP.FD -- solving the n-queens problem in Curry with FD constraints: queens :: [Option] -> Int -> [Int] queens options n = let qs = take n (domain 1 n) in solveFD options qs (allSafe qs) allSafe :: [FDExpr] -> FDConstr allSafe [] = true allSafe (q:qs) = safe q qs (fd 1) /\ allSafe qs safe :: FDExpr -> [FDExpr] -> FDExpr -> FDConstr safe _ [] _ = true safe q (q1:qs) p = no_attack q q1 p /\ safe q qs (p + fd 1) no_attack :: FDExpr -> FDExpr -> FDExpr -> FDConstr no_attack q1 q2 p = q1 /=# q2 /\ q1 /=# q2+p /\ q1 /=# q2-p ------------------------------------------------------------------------- ex1 = queens [] 8 ex2 = queens [FirstFail] 16