A way to avoid a common use of unsafePerformIO

Question

I often find this pattern in Haskell code:

options :: MVar OptionRecord
options = unsafePerformIO $ newEmptyMVar

...

doSomething :: Foo -> Bar
doSomethi         


        

Answer 1

If you are using MVar for holding settings or something similar, why don't you try reader monad?

foo :: ReaderT OptionRecord IO ()
foo = do
    options <- ask
    fireMissiles

main = runReaderT foo (OptionRecord "foo")

(And regular Reader if you don't require IO :P)