[GHC] #10331: Accept HsSyn in splices and generate it in quotes (ghc-api)
#10331: Accept HsSyn in splices and generate it in quotes (ghc-api) -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature | Status: new request | Milestone: Priority: low | Version: 7.11 Component: Template | Operating System: Unknown/Multiple Haskell | Type of failure: None/Unknown Keywords: | Blocked By: Architecture: | Related Tickets: Unknown/Multiple | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I propose a language pragma `GhcTemplateHaskell`, which, when enabled, causes Template Haskell splices to accept `HsSyn` return values, and causes TH quotes to return `HsSyn` trees. Users of `GhcTemplateHaskell` would stop using the `template-haskell` library and just directly manipulate the frontend ASTs using the `ghc-api`. Given our ghc-api track record, you would probably not be able to write code using this without having it break every GHC release. However, clients who are willing to track GHC development would reap the following benefits: 1. All syntax in Haskell would be supported in quotes; the AST would never lag behind. Additionally, you could use the ghc-api parser to parse Haskell code to be returned in a splice. (#2041) 2. Locations from quoting would be preserved. (Problem 2 of #10330) I don't think this would be difficult to implement, but it definitely could be a ball of wax. I broke this proposal off from #2041. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10331 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10331: Accept HsSyn in splices and generate it in quotes (ghc-api) -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Template Haskell | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by goldfire): I propose a slightly different direction: parameterize TH over the choice of AST. Something like {{{ class ExpAST e where repExp :: LHsExpr Name -> DsM (Core (TH.Q e)) cvExp :: e -> CvtM (LHsExpr RdrName) }}} Then, we define instances `ExpAST (LHsExpr Name)` and `ExpAST TH.Exp`. Perhaps the haskell-src-exts folks can define their own instance, too, if they so choose. I haven't thought this through, so apologies if this is a terrible idea. While we're moving in this direction, it might be nice to expose `TcM` to clients of TH. I know various terrible things could be done with the power of `TcM`, but nice things can, too. (In particular, I've wanted to be able to expand closed type families from TH code. I've implemented that functionality once [in GHC], and I dearly don't want to do it again! Exposing `TcM` would allow me to start thinking about how to do this.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10331#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10331: Accept HsSyn in splices and generate it in quotes (ghc-api) -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Template Haskell | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by simonpj): I'm utterly lost. To understand what is proposed here I need a lot more specifics and examples. For example * I think (though you do not say) that clients of the language extension would abandon all use of the `template-haskell` library. Instead they would depend on the `ghc` library. * I think that `[| e |]` would have type `Q (HsExpr RdrName)`. Etc etc. But it needs fleshing out or we'll all just talk at cross purposes. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10331#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10331: Accept HsSyn in splices and generate it in quotes (ghc-api) -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Template Haskell | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by goldfire): Yes, agreed about the fleshing out... but I don't have the bandwidth to get deeply involved in this upgrade to TH at the moment. I was just offering the idea of parameterizing via classes instead of making a monolithic change. I think the `ExpAST` thing would be no more work than the monolithic change originally proposed, but would be more flexible with little cost. That said, someone who actually wants to devote time into this is quite welcome to ignore my suggestion. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10331#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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