New type of ($) operator in GHC 8.0 is problematic

ghc-devs at ghc-devs at
Sat Feb 6 13:30:01 UTC 2016

Hi there,

I'm teaching Haskell to 2nd semester computer science students, and I
have been teaching Haskell since 2006.

While I certainly do appreciate the constant developement of Haskell,
and GHC, I'm becoming more and more concerned about the learning curve

For our students it is an entirely new concept that “Application” can
be an operator.  They are just learning about associativity.  `foldl`
and `foldr` are *baffling* concepts to them.  They have never thought
of functions being values.  They have never looked at a strict type

Having `Foldable` pop up last year already was not optimal, and to be
honest, this

    ($) :: forall (w :: Levity) a (b :: TYPE w). (a -> b) -> a -> b

is a disaster for teaching — Sorry.

Richard, thank you very much for your elaborate statement.  The
problem I see with a `BeginnersPrelude` is that it will either
outdate, or create a bubble escaping from which is so painful that
most new Haskell programmers will hesitate to take the step.  GHC
developement will carry on, more and more things being hidden behind
`BeginnersPrelude` automatically.  We will end up educating Beginners
that will want to stay beginners.

I'd personally wish for a `-fdefault-levity` switch, but I do not
oversee all the consequences right now.  I know it puts load on you,
but this actually just tells you that the language you're building
became a bit less learnable, maybe it's good to be aware of that.

Kind regards

--                                      o/X
Send plain text messages only, not exceeding 32kB.            /\/

More information about the ghc-devs mailing list