[Haskell-cafe] Generating random graph

[Mitar]

Hi!

I have made this function to generate a random graph for
Data.Graph.Inductive library:

generateGraph :: Int -> IO (Gr String Double)
generateGraph graphSize = do
  when (graphSize < 1) $ throwIO $ AssertionFailed $ "Graph size out
of bounds " ++ show graphSize
  let ns = map (\n -> (n, show n)) [1..graphSize]
  es <- fmap concat $ forM [1..graphSize] $ \node -> do
    nedges <- randomRIO (0, graphSize)
    others <- fmap (filter (node /=) . nub) $ forM [1..nedges] $ \_ ->
randomRIO (1, graphSize)
    gen <- getStdGen
    let weights = randomRs (1, 10) gen
    return $ zip3 (repeat node) others weights
  return $ mkGraph ns es

But I noticed that graph has sometimes same weights on different
edges. This is very unlikely to happen so probably I have some error
using random generators. Could somebody tell me where?


Mitar