[Haskell-cafe] Generating random graph

[Henning Thielemann]

On Mon, 11 Apr 2011, Mitar wrote:

> 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

Just a note on style: This function can perfectly be written without IO.

http://www.haskell.org/haskellwiki/Avoiding_IO#State_monad