Question

I was wondering if it’s possible to generate random tuples with a code like:

take 4 $ randomRs ((0,0),(70,100)) $ mkStdGen x  :: [(Double,Double)]

when I try this one I get the error:

No instance for (Random (Float, Float)) arising from a use of 'randoms'

Is there a way to get random tuples without using zip?

Answer 1

Basically the error message is saying that there isn’t a defined way of making random tuples. But you can of course add one yourself.

Off the top of my head (i.e., I haven’t actually tested this), you can do something like

instance (Random x, Random y) => Random (x, y) where
  randomR ((x1, y1), (x2, y2)) gen1 =
    let (x, gen2) = randomR (x1, x2) gen1
        (y, gen3) = randomR (y1, y2) gen2
    in ((x, y), gen3)

Now you can use randomR on tuples (provided that the types in the tuple support random generation).