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 xsbut 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.
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