Thanks Jakob -- but would it be possible to comment *on the ticket*, not here? (I should have said that more clearly.)
Simon On Thu, 13 Jul 2023 at 13:31, Jakob Brünker <jakob.bruen...@gmail.com> wrote: > Having written the MonadicBang plugin somewhat recently, where I don't > care about the exact-print annotations, I do have some snippets in my code > that look like this: > > AsPat xa name tok pat -> do > tellName name > AsPat xa name tok <$> traverse (liftMaybeT . evacPats) pat > > where the `tok` variable only exists to pass along the exact-print > annotations unchanged. So in that context, I would have a slight preference > for the exact-print annotations being hidden away in the extension points. > However, I think this also illustrates that the cost to clients is quite > manageable. Adding this one variable doesn't make the code unreadable - of > course, that's assuming exact-print annotations remain special and not just > the first in a long list of properties to eventually be added to each node. > > Of course, the cost *is* multiplied by the number of pattern matches on > AST nodes you have, which could be a lot given the amount of constructors > the types have. In my case, it was very few, because I was able to handle > the vast majority of constructors generically via the Data.Data instance. > > Jakob > > On Thu, Jul 13, 2023 at 1:23 PM Simon Peyton Jones < > simon.peytonjo...@gmail.com> wrote: > >> Dear GHC developers >> >> Could you please look at #23447 Where should "tokens" live >> <https://gitlab.haskell.org/ghc/ghc/-/issues/23447>? >> >> In brief, the question is whether we want to have: >> >> data HsExpr p = .... >> | HsLet (XLet p) (HsLocalBinds p) (LHsExpr p) >> or >> >> data HsExpr p = .... >> | HsLet (XLet p) (HsToken "let" p) >> (HsLocalBinds p) (HsToken "in" p) (LHsExpr p) >> >> >> In the former, if a client wants HsTokes to track the precise source >> locations of the "let" and "in" keywords, they'd have to put it in the TTG >> extension field; in the latter, this information is in *every* syntax >> tree. >> >> At the moment we have some of each, which is not satisfactory. We need to >> decide a policy and stick to it. If you use HsSyn, HsExpr, HsPat etc, in >> any way, you should have an opinion. Please do express it. At the moment >> we have only a few voices so we risk deciding without enough evidence and >> use-cases. >> >> Comments with specific use-cases and examples would be particularly >> helpful. >> >> Thanks! >> >> Simon >> >> _______________________________________________ >> ghc-devs mailing list >> ghc-devs@haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >> >
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