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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