为什么GHC认为这种类型的变量不是单射的?

I have this piece of code:

我有这段代码:

{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, KindSignatures, GADTs, FlexibleInstances, FlexibleContexts #-}

class Monad m => Effect p e r m | p e m -> r where
  fin :: p e m -> e -> m r

data ErrorEff :: * -> (* -> *) -> * where 
  CatchError :: (e -> m a) -> ErrorEff ((e -> m a) -> m a) m

instance Monad m => Effect ErrorEff ((e -> m a) -> m a) a m where
  fin (CatchError h) = \f -> f h
{-# LANG