Crypt Master,
CM> I have tried I swear, even googled for 45 minutes, but I
CM> cant seem to get random numbers working.
CM>
CM> In the documentation is has:
CM>
CM> rollDice :: IO Int
CM> rollDice = getStdRandom (randomR (1,6))
CM>
CM> But if I type "getStdRandom (randomR (1,6))" into hugs
CM> in the context of module which imports Random, I get get
CM> errors.
CM>
CM> ERROR - Unresolved overloading
CM> *** Type : (Random a, Num a) => IO a
CM> *** Expression : getStdRandom (randomR (1,6))
Use
(getStdRandom (randomR (1,6))) :: IO Int
instead.
\begin{code}
module Main where
import Random
main :: IO ()
main = do n <- (getStdRandom (randomR (1,6))) :: IO Int
; print n
\end{code}
Explanation. The compiler/interpreter knows your expressing is producing a
value of type IO a. It also knows a is an instance of Num. But it just does
not have enough information to resolve the exact type a. So, you have to
help the compiler/interpreter a little and provide the information it needs
through explicit type signatures or annotations.
HTH,
Stefan
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