unless you have some insanely clever refactoring tool ready that can convert pure into monadic functions and vice versa.
Not trying to attack the idea, just some thoughts: I don't see much problem converting pure function into an "effectfull" form :) Having pure function myPureFunction::a1->a2->a3->res .... myPureFunction a1 a2 a3 -- pure call myPureFunction <$> a1 <*> a2 <*> a3 -- call using Applicative Probably, introducing some conventions and using some language extensions you can write a function taking pure function and converting it into monadic version (a-la SPJ' work on polyvariadic composition etc [1]) Have monadic function but needs to call it from pure code? use Control.Monad.Identity. Not a big deal to me but maybe I'm missing the point ----- [1] http://okmij.org/ftp/Haskell/types.html#polyvar-comp