IOEnv
data IOEnv env a
failM
failWithM
data IOEnvFailure
getEnv
setEnv
updEnv
runIOEnv
unsafeInterleaveM
uninterruptibleMaskM_
tryM
tryAllM
tryMostM
fixM
data IORef a
newMutVar
readMutVar
writeMutVar
updMutVar
atomicUpdMutVar
atomicUpdMutVar'