From: Tobias Brandt <tob.brandt@googlemail.com>
Subject: Re: [Haskell-cafe] Type problems
To: "michael rice" <nowgate@yahoo.com>
Cc: haskell-cafe@haskell.org
Date: Saturday, July 24, 2010, 3:50 PM

You have to fix the type of 1 and 6, e.g. by writing

x <- randomRIO (1, 6) :: IO Int

or

x <- randomRIO (1, 6 :: Int)

 GHCi defaults integral numbers to Int, that's why it works there.

On 24 July 2010 21:36, michael rice <nowgate@yahoo.com> wrote:

This works: Prelude System.Random> do { randomRIO (1,6) >>= (\x -> putStrLn $ "Value = " ++ show x) } Value = 5 So does this: Prelude System.Random> do { x <- randomRIO (1,6); putStrLn $ "Value = " ++ show x } Value = 2 But not this: 1 import Control.Monad 2 import System.Random 3 4 foo :: IO () 5 foo = do 6   x <- randomRIO (1,6) 7   putStrLn $ "Value = " ++ show x foo.hs:6:18:     Ambiguous type variable `t' in the constraints:       `Num t' arising from the literal `1' at foo.hs:6:18       `Random t' arising from a use of `randomRIO' at foo.hs:6:7-21     Probable fix: add a type signature that fixes these type variable(s) Failed, modules loaded: none. Prelude System.Random> Or this: 1 import Control.Monad 2 import System.Random 3 4 foo :: IO () 5 foo = randomRIO (1,6) >>= (\x -> putStrLn $ "Value = " ++ show x) foo.hs:5:17:     Ambiguous type variable `t' in the constraints:       `Num t' arising from the literal `1' at foo.hs:5:17       `Random t' arising from a use of `randomRIO' at foo.hs:5:6-20     Probable fix: add a type signature that fixes these type variable(s) Failed, modules loaded: none. How to fix? Michael

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