#12390: List rules for `Coercible` instances -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): The Coercible class is special in other ways too, there is also [https://phabricator.haskell.org/diffusion/GHC/browse/master/libraries /ghc-prim/GHC/Types.hs;54c95ffcb2cf392df33d2ec397e2301c005ca406$84 no syntax for ~#R] {{{#!hs class a ~R# b => Coercible (a :: k) (b :: k) }}} making it difficult to get more information about `~R#`. (#12023) Some of this might be worth noting in `:info`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12390#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12390: List rules for `Coercible` instances -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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: | -------------------------------------+------------------------------------- Comment (by goldfire): +1 to comment:2. `Coercible` is not a class. Any resemblance it has to a class is purely historical. That said, I'm very sympathetic to the original motivation of having `:info Coercible` print something more useful. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12390#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12390: List rules for `Coercible` instances -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tellah): Newcomer here who has been poking around this a bit. From my initial impressions of the `:info` code, it would appear that the only place such an info string could be stored is in the TyThing. This is because the input string is converted String -> Name -> TyThing, and then the TyThing is converted to an IfaceDecl for printing. So then the question is: where does the suggested info string come from? I have some basic code that can store arbitrary text for `:info` but I am not sure what the front end for this should look like. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12390#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12390: List rules for `Coercible` instances -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: ghci059 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3634 Wiki Page: | -------------------------------------+------------------------------------- Changes (by tellah): * testcase: => ghci059 * status: new => patch * differential: => Phab:D3634 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12390#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12390: List rules for `Coercible` instances -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: tellah Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: ghci059 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3634 Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): The haddocks for Data.Coerce say it is a class, and include the ~R# constraint. Should this string also appear in the haddocks? Attaching the haddocks for Data.Coerce from HEAD. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12390#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12390: List rules for `Coercible` instances -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: tellah Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: ghci059 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3634 Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): Here are some design notes off the top of my head: I don't want to clutter `TyThing` with this, as it's unclear where within `TyThing` the documentation should go. In `TyCon`? Perhaps, but I don't love it. Instead, `InteractiveEval.getInfo` could return 5 things instead of 4; the fifth is an `SDoc` with extra text that should be printed. (It would normally be `empty`.) Naturally, you will have to add the fifth return value to `HscMain.hscTcRnGetInfo` and `TcRnDriver.tcRnGetInfo`. That last function can just call a new `lookupCustomDoc` function. That function can be defined in `PrelInfo`; it would refer to a `UniqFM SDoc` that associates `Unique`s with `SDoc`s. The `SDoc`s could (for now) just be hard-coded in `PrelInfo`. Certainly baked-in goodies other than `Coercible` can benefit from this new behavior. Perhaps it would be better to store the printed strings outside of a Haskell source file, but we don't have to over-design to begin with. Before implementing this, @tellah, perhaps someone else who is not a newcomer can opine on my design choices here. And, thanks! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12390#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12390: List rules for `Coercible` instances -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: tellah Type: bug | Status: closed Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: fixed | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: ghci059 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3634 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: patch => closed * resolution: => fixed * milestone: => 8.4.1 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12390#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler