Hi, Using the attached program: -------------------------------------------------------------------------------- D:\Temp>yhc Queens.hs Compiling Queens ( Queens.hs ) D:\Temp>yhi Queens.hbc Assertion failed: pinfo->info.tag == I_PINFO, file d:\sources\yhc\current\src\ru ntime\bckernel\mutins.h, line 295 This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information. -------------------------------------------------------------------------------- This also shows we have assertions on in the release "scons yhi" code, I guess they can stay in for now, but we really do need an optimisation mode. Program from Matt :-) Thanks Neil ----------- Queens.hs -------------- module Queens where main = nsoln 9 len :: [a] -> Int len [] = 0 len (x:xs) = 1 + len xs nsoln :: Int -> Int nsoln nq = len (gen nq) where gen :: Int -> [[Int]] gen 0 = [[]] gen n = [ (q:b) | b <- gen (n-1), q <- [1,2,3,4,5,6,7,8,9] {-toOne nq-}, safe q 1 b] safe :: Int -> Int -> [Int] -> Bool safe x d [] = True safe x d (q:l) = x /= q && x /= q+d && x /= q-d && safe x (d+1) l toOne :: Int -> [Int] toOne n = if n == 1 then [1] else n : toOne (n-1)