Re: Documenting record pattern synonyms

The documentation is in D1325 - https://phabricator.haskell.org/D1325 I added a specification to the wiki page - https://ghc.haskell.org/trac/ghc/wiki/PatternSynonyms/RecordPatternSynonyms On Thu, Oct 29, 2015 at 12:03 PM, Simon Peyton Jones wrote:

Matthew:

Could you please write the user-manual sections that you have promised? That is, the *specification* this feature.

Currently, so far as I can see, there is literally NO user manual documentation. No changes to docs/users_guide whatsoever.

We have discussed this on several occasions, and you agreed to do it. I sat with you in person and showed you what I have in mind. There is a sketch on the wiki page.

I did not intend this patch to land until the user documentation was done. Now I feel as if I've lost my leverage :-). But it really really really really needs doing.

Please. I'm begging you. Compared to what you have already done, it's easy.

Simon

| -----Original Message----- | From: ghc-commits [mailto:ghc-commits-bounces@haskell.org] On Behalf Of | git@git.haskell.org | Sent: 29 October 2015 11:25 | To: ghc-commits@haskell.org | Subject: [commit: ghc] master: Record pattern synonyms (2a74a64) | | Repository : ssh://git@git.haskell.org/ghc | | On branch : master | Link : | https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fghc.haskell. | org%2ftrac%2fghc%2fchangeset%2f2a74a64e8329ab9e0c74bec47198cb492d25affb%2fgh | c&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7c0deecf24e85641ff3abb08d2 | e05387f2%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=nEAgwVmvFQNgN%2bANGD4H | z1flN%2fucKSRFoZMdhRqQKSM%3d | | >--------------------------------------------------------------- | | commit 2a74a64e8329ab9e0c74bec47198cb492d25affb | Author: Matthew Pickering | Date: Mon Oct 19 21:17:29 2015 +0100 | | Record pattern synonyms | | This patch implements an extension to pattern synonyms which allows user | to specify pattern synonyms using record syntax. Doing so generates | appropriate selectors and update functions. | | === Interaction with Duplicate Record Fields === | | The implementation given here isn't quite as general as it could be with | respect to the recently-introduced `DuplicateRecordFields` extension. | | Consider the following module: | | {-# LANGUAGE DuplicateRecordFields #-} | {-# LANGUAGE PatternSynonyms #-} | | module Main where | | pattern S{a, b} = (a, b) | pattern T{a} = Just a | | main = do | print S{ a = "fst", b = "snd" } | print T{ a = "a" } | | In principle, this ought to work, because there is no ambiguity. But at | the moment it leads to a "multiple declarations of a" error. The problem | is that pattern synonym record selectors don't do the same name mangling | as normal datatypes when DuplicateRecordFields is enabled. They could, | but this would require some work to track the field label and selector | name separately. | | In particular, we currently represent datatype selectors in the third | component of AvailTC, but pattern synonym selectors are just represented | as Avails (because they don't have a corresponding type constructor). | Moreover, the GlobalRdrElt for a selector currently requires it to have | a parent tycon. | | (example due to Adam Gundry) | | === Updating Explicitly Bidirectional Pattern Synonyms === | | Consider the following | | ``` | pattern Silly{a} <- [a] where | Silly a = [a, a] | | f1 = a [5] -- 5 | | f2 = [5] {a = 6} -- currently [6,6] | ``` | | === Fixing Polymorphic Updates === | | They were fixed by adding these two lines in `dsExpr`. This might break | record updates but will be easy to fix. | | ``` | + ; let req_wrap = mkWpTyApps (mkTyVarTys univ_tvs) | | - , pat_wrap = idHsWrapper } | +, pat_wrap = req_wrap } | ``` | | === Mixed selectors error === | | Note [Mixed Record Field Updates] | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | | Consider the following pattern synonym. | | data MyRec = MyRec { foo :: Int, qux :: String } | | pattern HisRec{f1, f2} = MyRec{foo = f1, qux=f2} | | This allows updates such as the following | | updater :: MyRec -> MyRec | updater a = a {f1 = 1 } | | It would also make sense to allow the following update (which we | reject). | | updater a = a {f1 = 1, qux = "two" } ==? MyRec 1 "two" | | This leads to confusing behaviour when the selectors in fact refer the | same field. | | updater a = a {f1 = 1, foo = 2} ==? ??? | | For this reason, we reject a mixture of pattern synonym and normal | record selectors in the same update block. Although of course we still | allow the following. | | updater a = (a {f1 = 1}) {foo = 2} | | > updater (MyRec 0 "str") | MyRec 2 "str" | | | >--------------------------------------------------------------- | | 2a74a64e8329ab9e0c74bec47198cb492d25affb | compiler/basicTypes/ConLike.hs | 86 +++++++- | compiler/basicTypes/ConLike.hs-boot | 18 ++ | compiler/basicTypes/Id.hs | 31 ++- | compiler/basicTypes/IdInfo.hs | 21 +- | compiler/basicTypes/PatSyn.hs | 51 +++-- | compiler/deSugar/Coverage.hs | 11 +- | compiler/deSugar/DsExpr.hs | 79 ++++--- | compiler/deSugar/DsMeta.hs | 2 +- | compiler/hsSyn/Convert.hs | 10 +- | compiler/hsSyn/HsBinds.hs | 67 +++++- | compiler/hsSyn/HsExpr.hs | 35 +++- | compiler/hsSyn/HsUtils.hs | 21 +- | compiler/hsSyn/PlaceHolder.hs | 6 +- | compiler/iface/BuildTyCl.hs | 7 +- | compiler/iface/IfaceSyn.hs | 17 +- | compiler/iface/MkIface.hs | 11 +- | compiler/iface/TcIface.hs | 12 +- | compiler/main/HscTypes.hs | 15 +- | compiler/parser/Parser.y | 28 ++- | compiler/parser/RdrHsSyn.hs | 2 +- | compiler/prelude/TysWiredIn.hs | 2 +- | compiler/rename/RnBinds.hs | 18 +- | compiler/rename/RnExpr.hs | 8 +- | compiler/rename/RnNames.hs | 30 +-- | compiler/rename/RnSource.hs | 52 ++++- | compiler/typecheck/TcBinds.hs | 6 +- | compiler/typecheck/TcExpr.hs | 231 +++++++++++++++--- | --- | compiler/typecheck/TcHsSyn.hs | 10 +- | compiler/typecheck/TcPat.hs | 6 +- | compiler/typecheck/TcPatSyn.hs | 124 ++++++++--- | compiler/typecheck/TcPatSyn.hs-boot | 8 +- | compiler/typecheck/TcRnDriver.hs | 3 +- | compiler/typecheck/TcTyClsDecls.hs | 39 ++-- | compiler/types/TyCon.hs | 7 +- | compiler/types/TypeRep.hs | 2 +- | compiler/types/TypeRep.hs-boot | 1 + | testsuite/tests/patsyn/should_compile/all.T | 7 +- | .../tests/patsyn/should_compile/records-compile.hs | 11 + | .../tests/patsyn/should_compile/records-poly.hs | 16 ++ | .../patsyn/should_compile/records-prov-req.hs | 26 +++ | .../patsyn/should_compile/records-req-only.hs | 16 ++ | .../tests/patsyn/should_compile/records-req.hs | 14 ++ | testsuite/tests/patsyn/should_fail/all.T | 7 + | .../should_fail/mixed-pat-syn-record-sels.hs | 9 + | .../should_fail/mixed-pat-syn-record-sels.stderr | 5 + | .../tests/patsyn/should_fail/records-check-sels.hs | 10 + | .../patsyn/should_fail/records-check-sels.stderr | 3 + | .../tests/patsyn/should_fail/records-exquant.hs | 10 + | .../patsyn/should_fail/records-exquant.stderr | 11 + | .../patsyn/should_fail/records-mixing-fields.hs | 12 ++ | .../should_fail/records-mixing-fields.stderr | 17 ++ | .../patsyn/should_fail/records-no-uni-update.hs | 7 + | .../should_fail/records-no-uni-update.stderr | 5 + | .../patsyn/should_fail/records-no-uni-update2.hs | 11 + | .../should_fail/records-no-uni-update2.stderr | 5 + | .../patsyn/should_fail/records-poly-update.hs | 13 ++ | .../patsyn/should_fail/records-poly-update.stderr | 5 + | testsuite/tests/patsyn/should_run/all.T | 1 + | testsuite/tests/patsyn/should_run/records-run.hs | 14 ++ | .../tests/patsyn/should_run/records-run.stdout | 5 + | 60 files changed, 1055 insertions(+), 262 deletions(-) | | Diff suppressed because of size. To see it, use: | | git diff-tree --root --patch-with-stat --no-color --find-copies-harder - | -ignore-space-at-eol --cc 2a74a64e8329ab9e0c74bec47198cb492d25affb | _______________________________________________ | ghc-commits mailing list | ghc-commits@haskell.org | https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail.haskell | .org%2fcgi-bin%2fmailman%2flistinfo%2fghc- | commits&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7c0deecf24e85641ff3a | bb08d2e05387f2%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=ymzeKEsSAnOhr4QL | ngFKt0e8B84voue20%2bCyMPwWf%2fQ%3d