I think design A (deeply instantiate + generalize) produces the most sensible types. I don't know what the curly braces mean (perhaps that we can't use type application anymore since the order changed?) but I don't think they'd show up at all without -fprint-explicit-foralls, right? If so, I'm not too concerned about it. I also think 2C is a neat idea and should be explored further, but I don't think it should be the default behavior of :type. I've always expected :type to print the exact type we would infer for the expression. Perhaps instead of changing the default behavior of :type or adding new commands, we could add a flag to enhance :type's output. For example,
:type mapM mapM :: (Monad m, Traversable t) => (a -> m b) -> t a -> m (t b) :set -fprint-type-specializations :type mapM mapM :: (Monad m, Traversable t) => (a -> m b) -> t a -> m (t b) Possible Specializations: mapM :: Monad m => (a -> m b) -> [a] -> m [b] mapM :: (a -> Maybe b) -> [a] -> Maybe [b] ...
I think this could be useful even for experienced Haskellers, though I'm a bit concerned that printing the full type at the top will leave beginners as bewildered as ever.. Eric On Tue, Apr 26, 2016, at 06:08, Richard Eisenberg wrote:
Hi devs,
Over the weekend, I was pondering the Haskell course I will be teaching next year and shuddered at having to teach Foldable at the same time as `length`. So I implemented feature request #10963 (https://ghc.haskell.org/trac/ghc/ticket/10963), which allows for a way for a user to request a specialization of a type. It all works wonderfully, but there is a real user-facing design issue here around the default behavior of :type and whether or not to add new :type-y like commands. I have outlined the situation here: https://ghc.haskell.org/trac/ghc/wiki/Design/GHCi/Type
I'd love some broad input on this issue. If you've got a stake in how this all works, please skim that wiki page and comment on #10963.
Thanks! Richard _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs