#11081: Implement Introspective Template Haskell -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Template Haskell | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | TemplateHaskell/Introspective | -------------------------------------+------------------------------------- Changes (by jstolarek): * cc: jstolarek (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11081#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11081: Implement Introspective Template Haskell -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Template Haskell | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | TemplateHaskell/Introspective | -------------------------------------+------------------------------------- Comment (by lerkok): I think this is a great idea. In the past, I've tried both TH and haskell- src-exts to do relatively simple things, but ended-up abandoning them due to the inherent complexity of source level haskell that had very little to do with what I really cared about. Being able to get your hands on Core at the regular Haskell level would truly simplify life, and I suspect would open the flood-gates for a lot of people to develop extremely useful artifacts, making the GHC/Haskell experience even better. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11081#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11081: Implement Introspective Template Haskell -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Template Haskell | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | TemplateHaskell/Introspective | -------------------------------------+------------------------------------- Comment (by simonpj): I'm sceptical about the stuff about Core until I see more details. But that's for the future. The fundamental idea here is to replace `Language.Haskell.TH.Syntax` outright with `HsSyn`. The advantages, of course, are (a) avoiding duplication, (b) TH stop lagging GHC. The disadvantage is that `HsSyn` is designed as an internal data type for a compiler. We feel free to * decorate it with extra information (mostly types) as it moves down the pipeline, * have one constructor before type checking and a different one afterwards (eg `ConPatIn` and `ConPatOut` in `HsPat` * add elaboration info for type and dictionary applications and instantiation. For TH programs that construct syntax trees directly (ie not using quotation) or pattern-match over them, all this extra clutter might be confusing and/or awkward. I'm very unsure about the back-compat shim, but maybe it's possible. Yay for pattern synonyms. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11081#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11081: Implement Introspective Template Haskell -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Template Haskell | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | TemplateHaskell/Introspective | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Replying to [comment:5 simonpj]:

I'm very unsure about the back-compat shim, but maybe it's possible. Yay for pattern synonyms.

Could they also be used for other [https://ghc.haskell.org/trac/ghc/wiki/Migration/8.0?action=diff&version=42 migrations]? In [https://hackage.haskell.org/package/template- haskell-2.11.0.0/docs/Language-Haskell-TH-Lib.html#v:instanceD Language.Haskell.TH.Lib] another function `instanceWithOverlapD` was added to prevent breakage: {{{#!hs instanceD :: CxtQ -> TypeQ -> [DecQ] -> DecQ instanceWithOverlapD :: Maybe Overlap -> CxtQ -> TypeQ -> [DecQ] -> DecQ }}} The same could have been done with `InstanceD` {{{#!hs -- OLD: -- | InstanceD Cxt Type [Dec] | InstanceWithOverlapD (Maybe Overlap) Cxt Type [Dec] }}} and like `ErrorCall` defining {{{#!hs pattern InstanceD :: Ctx -> Type -> [Dec] -> Dec pattern InstanceD ctx ty decs = InstanceWithOverlapD Nothing ctx ty decs }}} which suffers from the [ticket:8779#comment:12 same problem] as `ErrorCall`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11081#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11081: Implement Introspective Template Haskell -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Template Haskell | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | TemplateHaskell/Introspective | -------------------------------------+------------------------------------- Comment (by goldfire): I think so, yes. Shayan Najd is currently completing a Summer of Haskell project (https://summer.haskell.org/) in an attempt to combine haskell- src-exts, GHC's `HsSyn`, and the TH AST. Serializability is a consideration, and so this should all be OK. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11081#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler