#10548: Support PartialTypeSignatures in Template Haskell -------------------------------------+------------------------------------- Reporter: spinda | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.10.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by spinda): I believe an implementation would consist of: (1) Add a {{{WildcardT (Maybe Name)}}} data constructor to the declaration of [https://github.com/ghc/ghc/blob/master/libraries/template- haskell/Language/Haskell/TH/Syntax.hs#L1464-L1483 Language.Haskell.TH.Syntax.Type]. (2) Add a new branch to [https://github.com/ghc/ghc/blob/058af6c90a0e8d122f2d1339b6b4fd0b5ec83d05/com... cvtTypeKind] that translates this to either [https://downloads.haskell.org/~ghc/latest/docs/html/libraries/ghc/HsTypes.ht... HsWildcardTy] or [https://downloads.haskell.org/~ghc/latest/docs/html/libraries/ghc/HsTypes.ht... HsNamedWildcardTy], depending on the {{{Maybe Name}}} value. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10548#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10548: Support PartialTypeSignatures in Template Haskell -------------------------------------+------------------------------------- Reporter: spinda | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.10.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by adamgundry): * cc: thomasw, adamgundry (added) Comment: I'd also like this (see #10094). I looked at it briefly and it didn't seem to be completely trivial, because the implementation traversed types to collect wildcards prior to renaming the type, and the presence of TH type splices means that it's hard to know up front whether wildcards will be present. But 058af6c90a0e8d122f2d1339b6b4fd0b5ec83d05 may have made it easier. Perhaps thomasw can advise further? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10548#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10548: Support PartialTypeSignatures in Template Haskell -------------------------------------+------------------------------------- Reporter: spinda | Owner: thomasw Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.10.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by thomasw): The changes to TH itself are straightforward. However Adam is right, the (named) wild cards must be known before renaming starts, and TH type splices are run ''during'' renaming. Besides a small bug I'm looking into, I see no problem with supporting anonymous wild cards in TH type splices. Named wild cards will require much more work and a refactoring of how splices and wild cards interact during renaming. Does it make sense to only allow anonymous wild cards in TH type splices but not named wild cards? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10548#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10548: Support PartialTypeSignatures in Template Haskell -------------------------------------+------------------------------------- Reporter: spinda | Owner: thomasw Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.10.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by adamgundry): Thanks for looking at this! I can't speak for everyone, but for my use case I need only anonymous type wild cards, not named or extra-constraints wild cards. Please do post a diff. We can perhaps put off the extra work until anyone comes up with a reason for wanting the other cases... -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10548#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10548: Support PartialTypeSignatures in Template Haskell -------------------------------------+------------------------------------- Reporter: spinda | Owner: thomasw Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.10.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: Phab:D1048 -------------------------------------+------------------------------------- Comment (by spinda): Ideally I'd like to see all type features accessible from TH, but this fits my use case right now. Thanks! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10548#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10548: Support PartialTypeSignatures in Template Haskell -------------------------------------+------------------------------------- Reporter: spinda | Owner: thomasw Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.10.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: Phab:D1048 -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"49373ffe4cbc87b46468d2372e850138e151a9ae/ghc" 49373ffe/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="49373ffe4cbc87b46468d2372e850138e151a9ae" Support wild cards in TH splices - Declaration splices: partial type signatures are fully supported in TH declaration splices. For example, the wild cards in the example below will unify with `Eq a` and `a -> a -> Bool`, as expected: ``` [d| foo :: _ => _ foo x y = x == y |] ``` - Expression splices: anonymous and named wild cards are supported in expression signatures, but extra-constraints wild cards aren't. Just as is the case for regular expression signatures. ``` [e | Just True :: _a _ |] ``` - Typed expression splices: the same wildcards as in (untyped) expression splices are supported. - Pattern splices: TH doesn't support type signatures in pattern splices, consequently, partial type signatures aren't supported either. - Type splices: partial type signatures are only partially supported in type splices, specifically: only anonymous wild cards are allowed. So `[t| _ |]`, `[t| _ -> Maybe _ |]` will work, but `[t| _ => _ |]` or `[| _a |]` won't (without `-XNamedWildCards`, the latter will work as the named wild card is treated as a type variable). Normally, named wild cards are collected before renaming a (partial) type signature. However, TH type splices are run during renaming, i.e. after the initial traversal, leading to out of scope errors for named wild cards. We can't just extend the initial traversal to collect the named wild cards in TH type splices, as we'd need to expand them, which is supposed to happen only once, during renaming. Similarly, the extra-constraints wild card is handled right before renaming too, and is therefore also not supported in a TH type splice. Another reason not to support extra-constraints wild cards in TH type splices is that a single signature can contain many TH type splices, whereas it mustn't contain more than one extra-constraints wild card. Enforcing would this be hard the way things are currently organised. Anonymous wild cards pose no problem, because they start without names and are given names during renaming. These names are collected right after renaming. The names generated for anonymous wild cards in TH type splices will thus be collected as well. With a more invasive refactoring of the renaming, partial type signatures could be fully supported in TH type splices. As only anonymous wild cards have been requested so far, these small changes satisfying this request will do for now. Also don't forget that a TH declaration splices support all kinds of wild cards. - Extra-constraints wild cards were silently ignored in expression and pattern signatures, appropriate error messages are now generated. Test Plan: run new tests Reviewers: austin, goldfire, adamgundry, bgamari Reviewed By: goldfire, adamgundry, bgamari Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D1048 GHC Trac Issues: #10094, #10548 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10548#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10548: Support PartialTypeSignatures in Template Haskell -------------------------------------+------------------------------------- Reporter: spinda | Owner: thomasw Type: feature request | Status: closed Priority: normal | Milestone: 7.12.1 Component: Template Haskell | Version: 7.10.1 Resolution: fixed | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: Phab:D1048 -------------------------------------+------------------------------------- Comment (by simonpj): Are there some feature tests for this? Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10548#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10548: Support PartialTypeSignatures in Template Haskell -------------------------------------+------------------------------------- Reporter: spinda | Owner: thomasw Type: feature request | Status: closed Priority: normal | Milestone: 7.12.1 Component: Template Haskell | Version: 7.10.1 Resolution: fixed | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: Phab:D1048 -------------------------------------+------------------------------------- Comment (by simonpj): Terrific. So can you add them to the "Test case" field of this ticket? Or if too many, list them in a comment, and in the "Test case" field say "see comment:23" of whatever? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10548#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler