bind has different semantics than fmap

[thurstonsand]

I may not understand the underlying reasoning, but fmap takes parameters f mv whereas bind takes mv f, so if you wanted to thread these it would be difficult. Is there a reason why the order is different?

[yurrriq]

As I understand it, cats is based (in part) on Haskell and its semantics. I've copied the relevant parts from GHC.Base here. N.B. >>= is pronounced bind.

class  Functor f  where
    fmap        :: (a -> b) -> f a -> f b

class Applicative m => Monad m where
    -- | Sequentially compose two actions, passing any value produced
    -- by the first as an argument to the second.
    (>>=)       :: forall a b. m a -> (a -> m b) -> m b

The code above shows fmap takes a function from a to b and an a wrapped in a functorial context f then returns a b wrapped in the same functorial context f.

>>= or bind on the other hand, takes a monadic action m a and a function from a to a monadic action m b then returns a monadic action m b.

[thurstonsand]

gotcha. makes sense to be consistent with haskell... still don't know the reasoning behind the different ordering tho

[ghost]

still don't know the reasoning behind the different ordering tho

No reason other than the signatures of the Haskell methods. I agree that is a bit inconsistent.