Re: [Haskell-cafe] MPTC and type classes issue (polymorphic '+')

input2 = [ InputDecs [ inp "emaLength" TyNumber (20 + 40) ] ]

(untested). Imho the simple, dumb, best fix for this is to give a explicit type to those values.

input2 = [ InputDecs [ inp "emaLength" TyNumber ((20::Integer) + (40::Integer)) ] ]

This is just one way to fix it. You could also try to improve your instances or enable -foverlapping-instances. But in my experience MPTC and overlapping instances, though powerful, can become very confusing, very quickly. Cheers pepe