> On Oct 27, 2021, at 9:54 AM, Benjamin Redelings > <benjamin.redeli...@gmail.com> wrote: > > Hi, > > I have been looking for info on what actually comes out of the > type-checking pass in GHC. This is mostly because it seems like the "Type > classes in Haskell" paper implements both type checking and translation to > dictionary-passing in one pass, whereas it seems like GHC separates this into > (i) type checking and (ii) desugaring.
This is correct: GHC takes two different passes to do this work. The big reason is around error messages: we want to have the code that the user wrote when reporting error messages. Since errors arise during type-checking, we thus want the output of the type checker to look like what the user wrote. > > Questions: > > 1. It seems like this separation is actually necessary, in order to apply > generalization only to let arguments written by the programmer, and not to > let bindings introduced during desugaring. Is that right? I don't think so. That is, if we did it all in one pass, I still think we could get generalization right. > > 2. Does the output of type checking contain type lambdas? Yes. See below. > > 3. Does the type checking pass determine where to add dictionary arguments? Yes. See below. > > 4. Are there any other resources I should be looking at? Yes. You want to enable -fprint-typechecker-elaboration (and possible -fprint-explicit-coercions). With the former, you get to see all this stuff you're looking for. It's normally suppressed so that the output resembles the user's code. I hope this helps! Richard _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
