I've stumbled over the following (code *extremely* simplified): f :: Bool f = g 1 g :: Num a => a -> Bool g _ = f This results in the following error message (on GHC): Contexts differ in length When matching the contexts of the signatures for f :: Bool g :: forall a. (Num a) => a -> Bool The signature contexts in a mutually recursive group should all be identical A similar problem is described in: darcs.haskell.org/haskore/docs/Tutorial.pdf on page 128. My first question is: 1) Is there a name for this restriction: I can't clearly identify it as some case of Let-Bound Polymorphism or the monomorphism restriction. [http://www.cs.auckland.ac.nz/references/haskell/haskell-intro-html/pitfalls....] 2) What exactly is the problem with it? 3) What's the best workaround? I've first tried to add an abundance of explicit type-annotations like f = (g::Int->Bool) 1 to it, but it doesn't work. Then, I found a solution, but it's awkward: f :: Bool f = g f 1 g :: Num a => Bool -> a -> Bool g f _ = f As you may have guessed, the actual code is a bit more complicated than this. Basically I interpret a symbol in a syntax-tree which can belong to different type-classes. When doing that, other more general symbols must be evaluated. An indirect recursion (potentially) occurs... I hope this hasn't been done to death yet. If it has, please just answer question one so that I can read up on it... Thank you, Tim