haskellmonad-transformersstate-monadstmio-monad

Haskell IO action in `StateT a STM b`

I want to run randomIO inside my StateT a STM b but I get this error:

Expected type: StateT Session STM Float
  Actual type: IO Float

so I try lift'ing from Control.Monad.Trans.Class (re-exported by State's Strict module):

Expected type: StateT Session STM Float
  Actual type: StateT Session IO Float

which is closer but not quite there. I can't liftIO because there's no MonadIO instance for STM.

How can I get this to compile so I can run randomIO inside STM inside my StateT?

Solution

  • As per the comments I was attempting something stupid. Instead I passed a list of random Floats that I needed to my function using randomRs (0.0, 1.0) g.