[Haskell-cafe] better way to do this?

Michael Mossey mpm at alumni.caltech.edu
Sun Oct 4 08:11:33 EDT 2009

Duncan Coutts wrote:
> On Sun, 2009-10-04 at 02:52 -0700, Michael Mossey wrote:
>> I'm looking for a hint to write the following code with less redundancy. I
>> have a constructor called BoxBounds, and I want to make one with random
>> values.
>> randomBox :: IO BoxBounds
>> randomBox = do
>>   x <- getStdRandom (randomR (-10,10))
>>   y <- getStdRandom (randomR (-70,70))
>>   t <- getStdRandom (randomR (5,10))
>>   b <- getStdRandom (randomR (5,10))
>>   l <- getStdRandom (randomR (5,10))
>>   r <- getStdRandom (randomR (5,10))
>>   return (BoxBounds x y l r t b)
> Others have already answered but I'd like to suggest that you avoid
> using IO here. There's no need for this to be impure. The getStdRandom
> function is one that should be avoided IMHO (and indeed removed from the
> Random module).
> A much nicer way to do the above is using some random monad, for example
> from the MonadRandom package. The suggestions from Felipe and Eugene
> will work just as well using Rand monad as the IO monad.
> Duncan

Hi Duncan,
Can you point me to a tutorial that covers the basics of randomness in 
Hasell? I find it very confusing.


More information about the Haskell-Cafe mailing list