-- | Construct queens on @n@ bells.
queens            :: Length -> Row
queens (Length n) = Row $ [fromInt 1, fromInt 3 .. fromInt n] ++ [fromInt 2, fromInt 4 .. fromInt n]
queens            :: Length -> Row
queens (Length n) = Row $ [fromInt 1, fromInt 3 .. fromInt n] ++ [fromInt 2, fromInt 4 .. fromInt n]
queens (Length n) = Row $ [fromInt 1, fromInt 3 .. fromInt n] ++ [fromInt 2, fromInt 4 .. fromInt n]