[Haskell-cafe] breadth first search one-liner?

Dear all, there is this neat "one-line" BFS implementation bfs :: Eq a => ( a -> [a] ) -> a -> [a] bfs next start = let xs = nub $ start : ( xs >>= next ) in xs but it has a problem: it only works for infinite graphs. This is fine: take 20 $ bfs ( \ x -> [2*x, x+1] ) 1 but this is not: take 20 $ bfs ( \ x -> filter (>0) [ div x 2, x - 1 ] ) 10 Is there a nice way to repair this? (I know how to code a BFS but here I'm asking for a one-liner.) J. W.