Maybe something like:

  class Foldable myFoldable where
    foldl :: (summary -> element -> summary) 
          -> summary 
          -> myFoldable element 
          -> summary

This is the translation I do in my head when I read that type signature, at least.

Wow. That's much better.

Apparently-idiomatic Haskell reads (or, rather, doesn't) about like line-noise/code-golf style Perl to me.

The problem with this is that there are Foldables that do not behave in the way that is implied by the above re-write of the parameters.

I think this is kind of the problem when you are really high up in abstraction-land. The functions that you're using are so generic that it's hard to say that they operate on anything in particular, except that the arguments fulfill certain properties or laws.

I wonder if anyone has worked on a Prelude replacement which has these replacements (along with renaming functions where appropriate)...

To change the names you'd have to re-implement all the functions. Good luck with that, base is /large/.

This is a documentation issue, not an implementation issue.

Really? I find the single-letter version far easier to read.

The single letter version is far easier since I already know what foldable does. Not so much when I'm learning a new library.

I've always disliked mapM_. Something about it just looks ugly and it doesn't really hint what its for. I would like to see mapM as mapMonad and mapM_ as eachMonad. Of course, once I knew what it meant the abbreviations became rather nice.