Can't spawn kernel from IHaskell notebook

[MMesch]

This example works very well on my machine:
https://github.com/gibiansky/jupyter-haskell/blob/master/examples/client-kernel-info/Main.hs

When I paste the same code into the IHaskell notebook (slightly adapted as shown below), the IHaskell notebook blocks after the spawnProcess call. Is there any way that allows to spawn a python kernel from the IHaskell notebook?

Cell1:

import           Control.Monad.IO.Class (MonadIO(liftIO))
import           System.Process (spawnProcess)

import           Data.Text (pack)
import           Jupyter.Client (runClient, sendClientRequest, ClientHandlers(..), connectKernel,
                                 defaultClientCommHandler, findKernel, writeProfile, Kernelspec(..))
import           Jupyter.Messages (ClientRequest(KernelInfoRequest), KernelReply(KernelInfoReply),
                                   KernelRequest(InputRequest), ClientReply(InputReply))

handlers :: ClientHandlers
handlers = ClientHandlers {
    commHandler = defaultClientCommHandler,
    kernelRequestHandler = \_ req ->
        case req of
        InputRequest{} -> return $ InputReply (pack "Fake Stdin"),
    kernelOutputHandler = \_ _ -> return ()
    }

Cell2

-- Find the kernelspec for the python 3 kernel
Just kernelspec <- findKernel (pack "python3")

-- Start the client connection
runClient Nothing Nothing handlers $ \profile -> do
    -- Write the profile connection file to a JSON file
    liftIO $ writeProfile profile "profile.json"

-- Launch the kernel process, giving it the path to the JSON file
let command = kernelspecCommand kernelspec "" "profile.json"
_ <- liftIO $ spawnProcess (head command) (tail command)

-- Send a kernel info request and get the reply
connection <- connectKernel
KernelInfoReply info <- sendClientRequest connection KernelInfoRequest
liftIO $ print info