[GHC] #10365: Make Semigroup as a superclass of Monoid
#10365: Make Semigroup as a superclass of Monoid -------------------------------------+------------------------------------- Reporter: gidyn | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.10.1 Component: | Operating System: Unknown/Multiple libraries/base | Type of failure: None/Unknown Keywords: | Blocked By: Architecture: | Related Tickets: Unknown/Multiple | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- See http://haskell.1045720.n5.nabble.com/Proposal-Make-Semigroup-as-a -superclass-of-Monoid-td5767835.html -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Make Semigroup as a superclass of Monoid -------------------------------------+------------------------------------- Reporter: gidyn | Owner: ekmett Type: feature request | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by gidyn): * owner: => ekmett -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Make Semigroup as a superclass of Monoid -------------------------------------+------------------------------------- Reporter: gidyn | Owner: ekmett Type: feature request | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.10.1 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 hvr): This topic just came up again over at http://www.reddit.com/r/haskell/comments/39tumu/make_semigroup_a_superclass_... ...and the associated previous reddit discussion for the proposal referenced in the ticket description can be found at http://www.reddit.com/r/haskell/comments/30s1t2/proposal_make_semigroup_as_a... -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Make Semigroup as a superclass of Monoid -------------------------------------+------------------------------------- Reporter: gidyn | Owner: ekmett Type: feature request | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by thomie): And `Data.List.NonEmpty` will be added, according to this [https://www.reddit.com/r/haskell/comments/3ipsc6/ghc_712_release_plan/cuk8dv... reddit comment by ekmett]. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Make Semigroup as a superclass of Monoid -------------------------------------+------------------------------------- Reporter: gidyn | Owner: ekmett Type: feature request | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by bergmark): * cc: bergmark (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Make Semigroup as a superclass of Monoid (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: ekmett Type: feature request | Status: new Priority: high | Milestone: 7.12.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report- | impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by hvr): * keywords: => report-impact * priority: normal => high * milestone: => 7.12.1 Old description:
See http://haskell.1045720.n5.nabble.com/Proposal-Make-Semigroup-as-a -superclass-of-Monoid-td5767835.html
New description: Last proposed in http://thread.gmane.org/gmane.comp.lang.haskell.libraries/24494 === Phase 1 (GHC 7.12) Phase 1 consists in (at the very least) moving `Data.Semigroup` and `Data.List.NonEmpty` into `base` for GHC 7.12 (aka 8.0). If there's enough time we will also implement a warning as part of the first phase:
Add a warning about definitions of an operator named `(<>)` that indicate it will be coming into Prelude in 7.14. We should warn about missing Semigroup instances at any use site of `(<>)` as they'll break in 7.14.
The rest of the migration roadmap is outlined in http://permalink.gmane.org/gmane.comp.lang.haskell.libraries/24526 -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: ekmett Type: feature request | Status: new Priority: high | Milestone: 7.12.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report- | impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Old description:
Last proposed in http://thread.gmane.org/gmane.comp.lang.haskell.libraries/24494
=== Phase 1 (GHC 7.12)
Phase 1 consists in (at the very least) moving `Data.Semigroup` and `Data.List.NonEmpty` into `base` for GHC 7.12 (aka 8.0).
If there's enough time we will also implement a warning as part of the first phase:
Add a warning about definitions of an operator named `(<>)` that indicate it will be coming into Prelude in 7.14. We should warn about missing Semigroup instances at any use site of `(<>)` as they'll break in 7.14.
The rest of the migration roadmap is outlined in http://permalink.gmane.org/gmane.comp.lang.haskell.libraries/24526
New description: More details in Proposal/SemigroupMonoid === Phase 1 (GHC 7.12) Phase 1 consists in (at the very least) moving `Data.Semigroup` and `Data.List.NonEmpty` into `base` for GHC 7.12 (aka 8.0). If there's enough time we will also implement a warning as part of the first phase:
Add a warning about definitions of an operator named `(<>)` that indicate it will be coming into Prelude in 7.14. We should warn about missing Semigroup instances at any use site of `(<>)` as they'll break in 7.14.
-- Comment (by hvr): added link to new Proposal/SemigroupMonoid wiki page (still a draft) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: Type: feature request | Status: new Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report- | impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by RyanGlScott): * cc: RyanGlScott (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: Type: feature request | Status: new Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): -------------------------------------+------------------------------------- Changes (by strake888): * Attachment "0001-add-Semigroup.patch" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: strake888 Type: feature request | Status: new Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): -------------------------------------+------------------------------------- Changes (by strake888): * owner: => strake888 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: strake888 Type: feature request | Status: new Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): -------------------------------------+------------------------------------- Comment (by hvr): I don't recognize the implementation, is this actually based on the the latest `semigroups` package release? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: strake888 Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): -------------------------------------+------------------------------------- Changes (by hvr): * status: new => patch -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: strake888 Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): -------------------------------------+------------------------------------- Comment (by ekmett): I'm not sure what is going on here with this patch. When I last checked we were looking at more or less porting the state of `semigroups` 0.17.0.1 directly into `base`. In fact that eas the reason for the 0.17 release, to get it into a state suitable for direct inclusion with a longer ramp-up period. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: hvr Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): -------------------------------------+------------------------------------- Changes (by hvr): * owner: strake888 => hvr Comment: @strake888, thanks for preparing the patch, but we had already planned out a much more elaborate patch (which I've just completed and published as Phab:D1284). I have to apologize as this was a miscommunication error on our end to remove the owner from this ticket and make it appear as if this task was looking for a volunteer. To be on the safe side in the future, please give a short heads-up notice if you see another task you may be interested in tackling, especially if the task description seems incomplete or still in work-in-progress state (as for this ticket). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: hvr Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 -------------------------------------+------------------------------------- Changes (by hvr): * differential: => Phab:D1284 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: hvr Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 -------------------------------------+------------------------------------- Comment (by strake888): Ah, cool. I merely saw this unowned with no patch and panicked cuz I '''seriously''' want this to happen this year. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: hvr Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 -------------------------------------+------------------------------------- Comment (by ekmett): All good. This served as a forcing function, driving us to flesh out the plan from start to finish and to get something ready for release. =) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1)
-------------------------------------+-------------------------------------
Reporter: gidyn | Owner: hvr
Type: feature request | Status: patch
Priority: high | Milestone: 8.0.1
Component: libraries/base | Version: 7.10.1
Resolution: | Keywords: report-impact
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D1284
-------------------------------------+-------------------------------------
Comment (by Herbert Valerio Riedel
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 -------------------------------------+------------------------------------- Changes (by hvr): * owner: hvr => quchen Comment: For the record, David is working on the warning-feature -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 -------------------------------------+------------------------------------- Comment (by bgamari): I realize that this has [[https://mail.haskell.org/pipermail/libraries/2015-May/025648.html|all been discussed before]] but I do wonder whether we really ''need'' to fold in `Data.List.NonEmpty` at this juncture? It does not appear to be a widely used type in practice and the interface has a few quirks. What do we gain by it being in `base`? The reason I ask is that I've noticed that `NonEmpty` introduces yet more partial functions to `base`. For instance, why must `words` have type `NonEmpty Char -> NonEmpty String`? Why not `NonEmpty Char -> [String]`? After all it seems quite reasonable for a non-empty string to nevertheless contain no words. Given that these are design decisions that reasonable people may disagree over, might it be best just to defer them packages outside of `base`? Sorry bringing this up so long after the initial consideration but I just wanted to make sure we have thoroughly considered this angle. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:20 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 -------------------------------------+------------------------------------- Comment (by bergmark): I would like to see the partial functions removed as well. toList is total, which makes fromList the most natural name for converting to a NonEmpty, but nope it's partial! Use nonEmpty instead. There's also a partial IsList instance, I really don't want literals to be able to crash at runtime. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:21 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 -------------------------------------+------------------------------------- Comment (by RyanGlScott): Replying to [comment:21 bergmark]:
I really don't want literals to be able to crash at runtime.
Bear in mind that it's already possible for literals to crash at runtime: {{{ $ ghci GHCi, version 7.10.2: http://www.haskell.org/ghc/ :? for help λ> import Numeric.Natural λ> -1 :: Natural *** Exception: arithmetic underflow }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:22 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 -------------------------------------+------------------------------------- Comment (by hvr): Replying to [comment:22 RyanGlScott]:
Bear in mind that it's already possible for literals to crash at runtime: {{{ λ> -1 :: Natural *** Exception: arithmetic underflow }}}
Somewhat related, #10930 wants GHC to at least emit a compiler warning in that case -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:23 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 -------------------------------------+------------------------------------- Comment (by RyanGlScott): Replying to [comment:23 hvr]:
Somewhat related, #10930 wants GHC to at least emit a compiler warning in that case
Ah, that's good to know. Perhaps we could add a similar warning for `[] :: NonEmpty` (when using `-XOverloadedLists`) in one of the phases of this proposal. While we're on this topic, I have another questions about things to come from the SMP (`Semigroup`–`Monoid` Proposal). Adding `Data.List.NonEmpty` brings in the `First`, `Last`, and `Option` data types, which are (intentionally) quite similar in behavior to `First` and `Last` (from `Data.Monoid`) and `Maybe`. Are there plans to consolidate (or strategically deprecate) some of these data types at some phase of the SMP? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:24 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): RyanGIScott: The plan around any sort of eventual consolidation of `First` and `Last` is definitely punted several years down the road. Once `Maybe` has the `Semigroup`-based `Monoid` instance, `Maybe (First a)` using the semigroup `First` has more or less the semantics of the existing monoidal `First a`. However, at this current moment such things have to be implemented in terms of `Option`, which is considerably more painful! After enough time has passed I can envision a situation where we might eventually choose to deprecate the existing Monoid versions, but that is far enough out that any proposal about it at this stage would be so much hand-waving. If it takes us 3 years to get `Semigroup` in as a superclass of `Monoid`, it'd likely take us another 3 years to get to where the new `Semigroup` forms of those constructions have wide enough distribution to even start considering deprecation of the originals. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:25 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): bgamari: Regarding `words`, that simply looks like a bug and it should have the type you've suggested. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:26 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
I would like to see the partial functions removed as well. toList is total, which makes fromList the most natural name for converting to a NonEmpty, but nope it's partial! Use nonEmpty instead. There's also a
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Lemming): Replying to [comment:21 bergmark]: partial IsList instance, I really don't want literals to be able to crash at runtime. In the non-empty package I fall back to infix operators for non-empty list construction. E.g. constructing a list with at least two elements looks like this: {{{0 !: 1 !: 2 : 3 : 4 : []}}}. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:27 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): @bgamari: I've removed words/unwords/lines/unlines. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:28 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1)
-------------------------------------+-------------------------------------
Reporter: gidyn | Owner: quchen
Type: feature request | Status: patch
Priority: high | Milestone: 8.0.1
Component: libraries/base | Version: 7.10.1
Resolution: | Keywords: report-impact
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D1284
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by Herbert Valerio Riedel
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by rwbarton): However, the real concern raised in #10365 is why Data.List.NonEmpty should be in base at all, causing extra work for GHC developers, and tying future fixes (once base is released) of this type to new versions of GHC, with no perceivable advantages. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:30 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): @rwbarton: The short version of it is this: We have `mconcat` for `Monoid` today. It actually sees a fair bit of use and I've seen folks implement it in the wild to do things like Kahan summation or better short circuiting than the base monoid can (it gets to assume an associativity.) `fold` gets to know the container, `mconcat` gets to know the Monoid. The moral equivalent in `Semigroup` requires some form of canonical non- empty type to fold over. The net effect of removing it is that the `semigroups` package would continue to exist just to supply this type, the class would lose its canonical structure to fold over, and `sconcat` becomes unimplementable. Why should moving `Semigroup` into `base` cost users functionality? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:31 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Lemming): Replying to [comment:31 ekmett]:
The moral equivalent in `Semigroup` requires some form of canonical non- empty type to fold over. The net effect of removing it is that the `semigroups` package would continue to exist just to supply this type, the class would lose its canonical structure to fold over, and `sconcat` becomes unimplementable.
`sconcat` in base could have type `s -> [s] -> s`. Then there is no need for `NonEmpty` to be in `base` and people can define top-level functions that use `sconcat` to implement a counterpart for their favourite `NonEmpty` type (e.g. `Data.List.NonEmpty` or `Data.NonEmpty`). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:32 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): Lemming: It is clear that any choice that includes it won't make you happy. However, randomly carving it up into two pieces and changing the API ensures that nobody who has existing code that supplies an `sconcat` in their instances winds up with code that will work across the transition. `semigroups` is the most downloaded package in all of Hackage, I don't like the idea of randomly bikeshedding the API here to get an end state that is less useful and which ensures work on the behalf of every package maintainer who currently implements `sconcat`. The transition story is better if we include it than if we don't, and the result is more usable out of the box. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:33 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by rwbarton): Yes, just give `sconcat` type `s -> [s] -> s`. A module being included in a package that is a dependency of a popular package is not a compelling reason to move that module into `base`! I mean I don't even know what to say to that. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:34 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): Both are reasonable colors for this bikeshed, but one doesn't break users. I'll refer this to the rest of the CLC to get a judgment. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:35 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by nomeata): I follow ekmett’s argument that Monoid to [] is like semigroups to ?, and to me it makes sense of have a type for non-empty sets in base. (If having a slim base were a goal, then maybe not, but I don’t see that being a goal for the community in general). But it is true that things are harder to fix once they are in base, so we should aim to pick the “right” implementation. According to https://wiki.haskell.org/Non-empty_list#Packages there are 6(!) implementations of non-empty lists on hackage. I did not look at them right now, so I’ll lazily pose the question: Is there any good reason to prefer any of these over the implementation from `semigroups`? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:36 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): @nomeata: FWIW- the implementation in `semigroups` was crafted by mixing and matching parts between the 2-3 implementations of non-empty lists at the time. The skeleton of it was build mostly by raiding the `NonEmptyList` package for parts with permission of the owners. AFAIK, Tony has deprecated his `NonEmptyList` package in favor of the one in `semigroups` (hence the lack of updates in the last 5 years -- this changeover predated having any deprecation mechanism on hackage.) Robin Kay's `NonEmpty` package is just a data type with no instances and no methods, also 6 years old. Cardinality also hasn't seen a patch in 6 years. Remarkably it still builds, because it too simply provides no instances. `MinLen` requires a ton of type system extensions. Out of the things that are suitable to consider as a `base`-ready encoding of a non-empty list, only Henning's `Data.NonEmpty` is actively maintained, and it tackles a more general problem, and brings with it a dozen different ad hoc classes for inserts and the like. So if you're hunting for materials to use to rebuild the bikeshed completely, I'd say out of the packages on hackage today, that is the only real source of lumber. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:37 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by nomeata): Right. `Data.NonEmpty` looks interesting, but a tad too interesting for a plain non-empty-list-type suitable for base. With all the others, the data type definition is equivalent, and rest of the API seems to be straight forward to me. So I have no qualms about this particular color of the shed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:38 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by rwbarton): You can rename the method of `Semigroup` with type `a -> [a] -> a` and move `sconcat` to a top-level definition in `Data.List.NonEmpty`, and that should hardly break anyone compared to the rather substantial `Semigroup => Monoid` superclass addition that is the main part of this proposal. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:39 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): @rwbarton: That is the most reasonable version of the "non-NonEmpty" version of the proposal I've heard. I'm not yet sold one way or the other, but I'll bring that up at the CLC meeting Thursday and see if that sways folks your way. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:40 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | prime:Libraries/Proposals/SemigroupMonoid| -------------------------------------+------------------------------------- Changes (by hvr): * wikipage: => prime:Libraries/Proposals/SemigroupMonoid Old description:
More details in Proposal/SemigroupMonoid
=== Phase 1 (GHC 7.12)
Phase 1 consists in (at the very least) moving `Data.Semigroup` and `Data.List.NonEmpty` into `base` for GHC 7.12 (aka 8.0).
If there's enough time we will also implement a warning as part of the first phase:
Add a warning about definitions of an operator named `(<>)` that indicate it will be coming into Prelude in 7.14. We should warn about missing Semigroup instances at any use site of `(<>)` as they'll break in 7.14.
New description: More details in prime:Libraries/Proposals/SemigroupMonoid === Phase 1 (GHC 7.12) Phase 1 consists in (at the very least) moving `Data.Semigroup` and `Data.List.NonEmpty` into `base` for GHC 7.12 (aka 8.0). If there's enough time we will also implement a warning as part of the first phase:
Add a warning about definitions of an operator named `(<>)` that indicate it will be coming into Prelude in 7.14. We should warn about missing Semigroup instances at any use site of `(<>)` as they'll break in 7.14.
-- Comment: update wiki page link -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:41 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | prime:Libraries/Proposals/SemigroupMonoid| -------------------------------------+------------------------------------- Comment (by bgamari): @ekmett, has there been any motion on this front? At this point I have no horse in this race; nevertheless I do want to make sure that whatever option we do end up with was chosen not by chance by but conscious decision. Sadly time is quickly running out for 8.0. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:42 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: patch Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | prime:Libraries/Proposals/SemigroupMonoid| -------------------------------------+------------------------------------- Comment (by nomeata): The committee decided to keep `sconcat`, and hence `NonEmpty`: https://prime.haskell.org/wiki/Libraries/Meetings/2015-11-05 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:43 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: closed Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: fixed | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | prime:Libraries/Proposals/SemigroupMonoid| -------------------------------------+------------------------------------- Changes (by bgamari): * status: patch => closed * resolution: => fixed Comment: Alright then. I believe this issue is then resolved. Thanks everyone! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:44 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: closed Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: fixed | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1284 Wiki Page: | prime:Libraries/Proposals/SemigroupMonoid| -------------------------------------+------------------------------------- Comment (by quchen): AMP for Semigroup is in review status on Phab:D1539, Trac #11139 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:45 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10365: Implement Semigroup as a superclass of Monoid Proposal (Phase 1) -------------------------------------+------------------------------------- Reporter: gidyn | Owner: quchen Type: feature request | Status: closed Priority: high | Milestone: 8.0.1 Component: libraries/base | Version: 7.10.1 Resolution: fixed | Keywords: report-impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #14191 | Differential Rev(s): Phab:D1284 Wiki Page: | prime:Libraries/Proposals/SemigroupMonoid| -------------------------------------+------------------------------------- Changes (by hvr): * related: => #14191 Comment: Phase 2 is tracked in #14191 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10365#comment:46 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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