[Haskell-cafe] Generate 50 random coordinates
dagit at codersbase.com
Sat Dec 2 02:41:05 EST 2006
On 12/1/06, Huazhi (Hank) Gong <hankgong at nm.gist.ac.kr> wrote:
> My intention is to generate 50 random coordinates like (x,y).
> myrand :: Int
> myrand = randomRIO(1::Int, 100)
When we look at the type of randomRIO we see:
randomRIO :: forall a. (Random a) => (a, a) -> IO a
You're giving it a tuple of Int, so we can substitute Int for 'a' in
that type signature:
myrand :: IO Int
> rf=[(myrand, myrand) | a <- [1..50]]
Here you are creating a list of tuples. We see from above that the
type of the tuples would be (IO Int, IO Int), so rf :: [(IO Int, IO
Int)]. This is because we have not run the IO action to generate the
> My short program is like this. However, GHCI say that the return type of
> randomRIO is IO a while the function defined by me is Int. Since I only need
> a integral type as my cooridinate, could you tell me how to fix this?
Your type signature tries to make a claim that myrand has type Int,
but the compiler will disagree because of that pesky IO type.
Yet Another Haskell Tutorial seems to have a section on the pesky IO type.
I hope that helps,
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