How to print the results of sampling an RVar - haskell

Question

I have a program that works. However, I wasn't exactly sure why it was compiling.
Here's my main function
module Main where
import System.Environment
import Cover5
main :: IO ()
main = do
args <- getArgs
let numGames = if null args then 13 else read $ head args
putStrLn $ "Making picks for " ++ show numGames ++ " games."
print $ run numGames
where the function run has the signature run :: Int -> RVar [(Int, Char)].
What is confusing is that there is no instance of Show for RVar [(Int,Char)] so I figure it shouldn't compile, but it does (see Travis-CI build and the related source for that commit of Main.hs). I can force a warning with this command:
cabal build --ghc-options="-fforce-recomp -fno-code"
Preprocessing executable 'cover5' for cover5-0.1.0.1...
[1 of 2] Compiling Cover5 ( src/Cover5.hs, nothing )
[2 of 2] Compiling Main ( src/Main.hs, nothing )
src/Main.hs:13:10: error:
• No instance for (Show (RVar [(Int, Char)]))
arising from a use of ‘print’
• In a stmt of a 'do' block: print $ run numGames
In the expression:
do { args <- getArgs;
let numGames = ...;
putStrLn $ "Making picks for " ++ show numGames ++ " games.";
print $ run numGames }
In an equation for ‘main’:
main
= do { args <- getArgs;
let numGames = ...;
putStrLn $ "Making picks for " ++ show numGames ++ " games.";
.... }
I'd like to "fix" this and have followed guidance from the question Convert Data.RVar.RVar [Char] to [Char]
So I add the appropriate imports for StdRandom and runRVar and write the following lines
results <- runRVar (run numGames) StdRandom
putStrLn $ show results
But I'm tripping over myself trying to find instances of MonadRandom IO for my usage:
src/Main.hs:13:21: error:
• No instance for (MonadRandom IO) arising from a use of ‘runRVar’
• In a stmt of a 'do' block:
results <- runRVar (run numGames) StdRandom
In the expression:
do { args <- getArgs;
let numGames = ...;
putStrLn $ "Making picks for " ++ show numGames ++ " games.";
results <- runRVar (run numGames) StdRandom;
.... }
In an equation for ‘main’:
main
= do { args <- getArgs;
let numGames = ...;
putStrLn $ "Making picks for " ++ show numGames ++ " games.";
.... }
So two questions:
Why does the original version compile and work?
What might you suggest I do to remove the warning and write this "correctly"?

Answer 1

The answer(s) were provided by #leftaroundabout in the comments. Posting an answer here for others new to Random in case it proves helpful
First Question
I had written the original program about 3 years ago. I had no idea how to print results from RVars. I chose to use Data.Random.Show.Unsafe. Apparently this module provides an instance of Show for RVar a. I didn't remember that.
In addition, I was implicitly exporting everything from my Cover5 module so the main module whose code is above was importing that instance.
So that's why print was working.
Second Question
Instances are available in Data.Random, which I wasn't importing.
The reason why I was getting errors but was thinking they were warnings is because I changed 2 (actually more than 2) things at once:
I restricted what was exported from Cover5 module so the Unsafe
instance of Show wasn't exported anymore
I ran the build with some arguments which I thought were just going to show more warnings than a traditional build.