1. 18 Jan, 2016 1 commit
    • Eric Seidel's avatar
      un-wire-in error, undefined, CallStack, and IP · a7b751db
      Eric Seidel authored and Ben Gamari's avatar Ben Gamari committed
      I missed a crucial step in the wiring-in process of `CallStack` in D861,
      the bit where you actually wire-in the Name... This led to a nasty bug
      where GHC thought `CallStack` was not wired-in and tried to fingerprint
      it, which failed because the defining module was not loaded.
      
      But we don't need `CallStack` to be wired-in anymore since `error` and
      `undefined` no longer need to be wired-in. So we just remove them all.
      
      Updates haddock submodule.
      
      Test Plan: `./validate` and `make slowtest TEST=tc198`
      
      Reviewers: simonpj, goldfire, austin, hvr, bgamari
      
      Reviewed By: simonpj, bgamari
      
      Subscribers: goldfire, thomie
      
      Projects: #ghc
      
      Differential Revision: https://phabricator.haskell.org/D1739
      
      GHC Trac Issues: #11331
      a7b751db
  2. 15 Jan, 2016 1 commit
    • eir@cis.upenn.edu's avatar
      Fix #10872. · d459f55c
      eir@cis.upenn.edu authored
      This moves the duplicate-unique check from knownKeyNames (which omits
      TH) to allKnownKeyNames (which includes TH).
      d459f55c
  3. 13 Jan, 2016 1 commit
    • Ben Gamari's avatar
      Add missing type representations · ac3cf68c
      Ben Gamari authored and Ben Gamari's avatar Ben Gamari committed
      Previously we were missing `Typeable` representations for several
      wired-in types (and their promoted constructors). These include,
      
       * `Nat`
       * `Symbol`
       * `':`
       * `'[]`
      
      Moreover, some constructors were incorrectly identified as being defined
      in `GHC.Types` whereas they were in fact defined in `GHC.Prim`.
      
      Ultimately this is just a temporary band-aid as there is general
      agreement that we should eliminate the manual definition of these
      representations entirely.
      
      Test Plan: Validate
      
      Reviewers: austin, hvr
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1769
      
      GHC Trac Issues: #11120
      ac3cf68c
  4. 07 Jan, 2016 1 commit
    • Simon Peyton Jones's avatar
      Make demand analysis understand catch · 9915b656
      Simon Peyton Jones authored
      As Trac #11222, and #10712 note, the strictness analyser
      needs to be rather careful about exceptions.  Previously
      it treated them as identical to divergence, but that
      won't quite do.
      
      See Note [Exceptions and strictness] in Demand, which
      explains the deal.
      
      Getting more strictness in 'catch' and friends is a
      very good thing.  Here is the nofib summary, keeping
      only the big ones.
      
      --------------------------------------------------------------------------------
              Program           Size    Allocs   Runtime   Elapsed  TotalMem
      --------------------------------------------------------------------------------
                fasta          -0.1%     -6.9%     -3.0%     -3.0%     +0.0%
                  hpg          -0.1%     -2.0%     -6.2%     -6.2%     +0.0%
             maillist          -0.1%     -0.3%      0.08      0.09     +1.2%
      reverse-complem          -0.1%    -10.9%     -6.0%     -5.9%     +0.0%
               sphere          -0.1%     -4.3%      0.08      0.08     +0.0%
                 x2n1          -0.1%     -0.0%      0.00      0.00     +0.0%
      --------------------------------------------------------------------------------
                  Min          -0.2%    -10.9%    -17.4%    -17.3%     +0.0%
                  Max          -0.0%     +0.0%     +4.3%     +4.4%     +1.2%
       Geometric Mean          -0.1%     -0.3%     -2.9%     -3.0%     +0.0%
      
      On the way I did quite a bit of refactoring in Demand.hs
      9915b656
  5. 01 Jan, 2016 1 commit
    • Herbert Valerio Riedel's avatar
      Canonicalise `MonadPlus` instances · dafeb51f
      Herbert Valerio Riedel authored
      This refactoring exploits the fact that since AMP, in most cases,
      `instance MonadPlus` can be automatically derived from the respective
      `Alternative` instance.  This is because `MonadPlus`'s default method
      implementations are fully defined in terms of `Alternative(empty, (<>))`.
      dafeb51f
  6. 31 Dec, 2015 2 commits
  7. 24 Dec, 2015 2 commits
    • eir@cis.upenn.edu's avatar
      Visible type application · 2db18b81
      eir@cis.upenn.edu authored
      This re-working of the typechecker algorithm is based on
      the paper "Visible type application", by Richard Eisenberg,
      Stephanie Weirich, and Hamidhasan Ahmed, to be published at
      ESOP'16.
      
      This patch introduces -XTypeApplications, which allows users
      to say, for example `id @Int`, which has type `Int -> Int`. See
      the changes to the user manual for details.
      
      This patch addresses tickets #10619, #5296, #10589.
      2db18b81
    • Simon Peyton Jones's avatar
      Refactoring only · 1af0d36b
      Simon Peyton Jones authored
      This moves code around to more sensible places.
      
      - Construction for CoAxiom is localised in FamInstEnv
      
      - orphNamesOfxx moves to CoreFVs
      
      - roughMatchTcs, instanceCantMatch moves to Unify
      
      - mkNewTypeCo moves from Coercion to FamInstEnv, and is
        renamed mkNewTypeCoAxiom, which makes more sense
      1af0d36b
  8. 23 Dec, 2015 2 commits
    • Eric Seidel's avatar
      Allow CallStacks to be frozen · 380b25ea
      Eric Seidel authored and Ben Gamari's avatar Ben Gamari committed
      This introduces "freezing," an operation which prevents further
      locations from being appended to a CallStack.  Library authors may want
      to prevent CallStacks from exposing implementation details, as a matter
      of hygiene. For example, in
      
      ```
      head [] = error "head: empty list"
      
      ghci> head []
      *** Exception: head: empty list
      CallStack (from implicit params):
        error, called at ...
      ```
      
      including the call-site of `error` in `head` is not strictly necessary
      as the error message already specifies clearly where the error came
      from.
      
      So we add a function `freezeCallStack` that wraps an existing CallStack,
      preventing further call-sites from being pushed onto it. In other words,
      
      ```
      pushCallStack callSite (freezeCallStack callStack) = freezeCallStack callStack
      ```
      
      Now we can define `head` to not produce a CallStack at all
      
      ```
      head [] =
        let ?callStack = freezeCallStack emptyCallStack
        in error "head: empty list"
      
      ghci> head []
      *** Exception: head: empty list
      CallStack (from implici...
      380b25ea
    • Simon Peyton Jones's avatar
      Fix super-class cycle check · f13de71b
      Simon Peyton Jones authored
      Fixes Trac #11278
      f13de71b
  9. 22 Dec, 2015 2 commits
    • Simon Peyton Jones's avatar
      Refactor named wildcards (again) · 575a98e4
      Simon Peyton Jones authored
      Michal's work on #10982, #11098, refactored the handling of named
      wildcards by making them more like ordinary type variables.
      
      This patch takes the same idea to its logical conclusion, resulting
      in a much tidier, tighter implementation.
      
      Read Note [The wildcard story for types] in HsTypes.
      
      Changes:
      
       * Named wildcards are ordinary type variables, throughout
      
       * HsType no longer has a data constructor for named wildcards
         (was NamedWildCard in HsWildCardInfo).  Named wildcards are
         simply HsTyVars
      
       * Similarly named wildcards disappear from Template Haskell
      
       * I refactored RnTypes to avoid polluting LocalRdrEnv with something
         as narrow as named wildcards.  Instead the named wildcard set is
         carried in RnTyKiEnv.
      
      There is a submodule update for Haddock.
      575a98e4
    • Ryan Scott's avatar
      Rework Template Haskell's handling of strictness · f975b0b1
      Ryan Scott authored and Ben Gamari's avatar Ben Gamari committed
      Currently, Template Haskell's treatment of strictness is not enough to
      cover all possible combinations of unpackedness and strictness. In
      addition, it isn't equipped to deal with new features (such as
      `-XStrictData`) which can change a datatype's fields' strictness during
      compilation.
      
      To address this, I replaced TH's `Strict` datatype with
      `SourceUnpackedness` and `SourceStrictness` (which give the programmer a
      more complete toolkit to configure a datatype field's strictness than
      just `IsStrict`, `IsLazy`, and `Unpack`). I also added the ability to
      reify a constructor fields' strictness post-compilation through the
      `reifyConStrictness` function.
      
      Fixes #10697.
      
      Test Plan: ./validate
      
      Reviewers: simonpj, goldfire, bgamari, austin
      
      Reviewed By: goldfire, bgamari
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1603
      
      GHC Trac Issues: #10697
      f975b0b1
  10. 21 Dec, 2015 3 commits
    • Jan Stolarek's avatar
      Add proper GADTs support to Template Haskell · eeecb864
      Jan Stolarek authored
      Until now GADTs were supported in Template Haskell by encoding them using
      normal data types.  This patch adds proper support for representing GADTs
      in TH.
      
      Test Plan: T10828
      
      Reviewers: goldfire, austin, bgamari
      
      Subscribers: thomie, mpickering
      
      Differential Revision: https://phabricator.haskell.org/D1465
      
      GHC Trac Issues: #10828
      eeecb864
    • Simon Marlow's avatar
      Maintain cost-centre stacks in the interpreter · c8c44fd9
      Simon Marlow authored
      Summary:
      Breakpoints become SCCs, so we have detailed call-stack info for
      interpreted code.  Currently this only works when GHC is compiled with
      -prof, but D1562 (Remote GHCi) removes this constraint so that in the
      future call stacks will be available without building your own GHCi.
      
      How can you get a stack trace?
      
      * programmatically: GHC.Stack.currentCallStack
      * I've added an experimental :where command that shows the stack when
        stopped at a breakpoint
      * `error` attaches a call stack automatically, although since calls to
        `error` are often lifted out to the top level, this is less useful
        than it might be (ImplicitParams still works though).
      * Later we might attach call stacks to all exceptions
      
      Other related changes in this diff:
      
      * I reduced the number of places that get ticks attached for
        breakpoints.  In particular there was a breakpoint around the whole
        declaration, which was often redundant because it bound no variables.
        This reduces clutter in the stack traces and speeds up compilation.
      
      * I tidied up some RealSrcSpan stuff in InteractiveUI, and made a few
        other small cleanups
      
      Test Plan: validate
      
      Reviewers: ezyang, bgamari, austin, hvr
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1595
      
      GHC Trac Issues: #11047
      c8c44fd9
    • Ryan Scott's avatar
      Encode strictness in GHC generics metadata · ee6fba89
      Ryan Scott authored and Ben Gamari's avatar Ben Gamari committed
      This augments `MetaSel` with a `Bang` field, which gives generic
      programmers access to the following information about each field
      selector:
      
      * `SourceUnpackedness`: whether a field was marked `{-# NOUNPACK #-}`,
        `{-# UNPACK #-}`, or not
      * `SourceStrictness`: whether a field was given a strictness (`!`) or
        laziness (`~`) annotation
      * `DecidedStrictness`: what strictness GHC infers for a field during
        compilation, which may be influenced by optimization levels,
        `-XStrictData`, `-funbox-strict-fields`, etc.
      
      Unlike in Phab:D1603, generics does not grant a programmer the ability
      to "splice" in metadata, so there is no issue including
      `DecidedStrictness` with `Bang` (whereas in Template Haskell, it had to
      be split off).
      
      One consequence of this is that `MetaNoSel` had to be removed, since it
      became redundant. The `NoSelector` empty data type was also removed for
      similar reasons.
      
      Fixes #10716.
      
      Test Plan: ./validate
      
      Reviewers: dreixel, goldfire, kosmikus, aust...
      ee6fba89
  11. 18 Dec, 2015 1 commit
  12. 16 Dec, 2015 1 commit
  13. 15 Dec, 2015 4 commits
    • Ben Gamari's avatar
      primops: Mark actions evaluated by `catch*` as lazy · 28638dfe
      Ben Gamari authored and Ben Gamari's avatar Ben Gamari committed
      There is something very peculiar about the `catch` family of operations
      with respect to strictness analysis: they turn divergence into
      non-divergence. For this reason, it isn't safe to mark them as strict in
      the expression whose exceptions they are catching. The reason is this:
      
      Consider,
      
          let r = \st -> raiseIO# blah st
          in catch (\st -> ...(r st)..) handler st
      
      If we give the first argument of catch a strict signature, we'll get a
      demand 'C(S)' for 'r'; that is, 'r' is definitely called with one
      argument, which indeed it is. The trouble comes when we feed 'C(S)' into
      'r's RHS as the demand of the body as this will lead us to conclude that
      the whole 'let' will diverge; clearly this isn't right.
      
      This is essentially the problem in #10712, which arose when
      7c0fff41 marked the `catch*` primops as
      being strict in the thing to be evaluated. Here I've partially reverted
      this commit, again marking the first argument of these primops as lazy.
      
      Fixes #10712.
      
      Test Plan: Validate checking `exceptionsrun001`
      
      Reviewers: simonpj, austin
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1616
      
      GHC Trac Issues: #10712, #11222
      28638dfe
    • Ben Gamari's avatar
      Narrow scope of special-case for unqualified printing of names in core libraries · e2c91738
      Ben Gamari authored and Ben Gamari's avatar Ben Gamari committed
      Commit 547c5971 modifies the
      pretty-printer to render names from a set of core packages (`base`,
      `ghc-prim`, `template-haskell`) as unqualified. The idea here was that
      many of these names typically are not in scope but are well-known by the
      user and therefore qualification merely introduces noise.
      
      This, however, is a very large hammer and potentially breaks any
      consumer who relies on parsing GHC output (hence #11208). This commit
      partially reverts this change, now only printing `Constraint` (which
      appears quite often in errors) as unqualified.
      
      Fixes #11208.
      
      Updates tests in `array` submodule.
      
      Test Plan: validate
      
      Reviewers: hvr, thomie, austin
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1619
      
      GHC Trac Issues: #11208
      e2c91738
    • Simon Peyton Jones's avatar
      Comments on equality types and classes · b8ca6459
      Simon Peyton Jones authored
      This is really just doucumenting one aspect of the kind-equality patch.
      
      See especially Note [Equality types and classes] in TysWiredIn.
      Other places should just point to this Note.
      
      Richard please check for veracity.
      b8ca6459
    • Ömer Sinan Ağacan's avatar
  14. 12 Dec, 2015 1 commit
    • Edward Z. Yang's avatar
      Frontend plugins. · a3c2a26b
      Edward Z. Yang authored
      
      
      Summary:
      Frontend plugins enable users to write plugins to replace
      GHC major modes.  E.g. instead of saying
      
          ghc --make A B C
      
      a user can now say
      
          ghc --frontend GHC.Frontend.Shake A B C
      
      which might provide an alternative implementation of a multi-module
      build.  For more details, see the manual entry.
      
      Signed-off-by: default avatarEdward Z. Yang <ezyang@cs.stanford.edu>
      
      Test Plan: validate
      
      Reviewers: simonmar, bgamari, austin, simonpj
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1598
      
      GHC Trac Issues: #11194
      a3c2a26b
  15. 11 Dec, 2015 1 commit
    • eir@cis.upenn.edu's avatar
      Add kind equalities to GHC. · 67465497
      eir@cis.upenn.edu authored
      This implements the ideas originally put forward in
      "System FC with Explicit Kind Equality" (ICFP'13).
      
      There are several noteworthy changes with this patch:
       * We now have casts in types. These change the kind
         of a type. See new constructor `CastTy`.
      
       * All types and all constructors can be promoted.
         This includes GADT constructors. GADT pattern matches
         take place in type family equations. In Core,
         types can now be applied to coercions via the
         `CoercionTy` constructor.
      
       * Coercions can now be heterogeneous, relating types
         of different kinds. A coercion proving `t1 :: k1 ~ t2 :: k2`
         proves both that `t1` and `t2` are the same and also that
         `k1` and `k2` are the same.
      
       * The `Coercion` type has been significantly enhanced.
         The documentation in `docs/core-spec/core-spec.pdf` reflects
         the new reality.
      
       * The type of `*` is now `*`. No more `BOX`.
      
       * Users can write explicit kind variables in their code,
         anywhere they can write type variables. ...
      67465497
  16. 07 Dec, 2015 1 commit
  17. 03 Dec, 2015 1 commit
    • Georgios Karachalias's avatar
      Major Overhaul of Pattern Match Checking (Fixes #595) · 8a506104
      Georgios Karachalias authored
      This patch adresses several problems concerned with exhaustiveness and
      redundancy checking of pattern matching. The list of improvements includes:
      
      * Making the check type-aware (handles GADTs, Type Families, DataKinds, etc.).
        This fixes #4139, #3927, #8970 and other related tickets.
      
      * Making the check laziness-aware. Cases that are overlapped but affect
        evaluation are issued now with "Patterns have inaccessible right hand side".
        Additionally, "Patterns are overlapped" is now replaced by "Patterns are
        redundant".
      
      * Improved messages for literals. This addresses tickets #5724, #2204, etc.
      
      * Improved reasoning concerning cases where simple and overloaded
        patterns are matched (See #322).
      
      * Substantially improved reasoning for pattern guards. Addresses #3078.
      
      * OverloadedLists extension does not break exhaustiveness checking anymore
        (addresses #9951). Note that in general this cannot be handled but if we know
        that an argument has type '[...
      8a506104
  18. 01 Dec, 2015 1 commit
    • Simon Peyton Jones's avatar
      Refactor treatment of wildcards · 1e041b73
      Simon Peyton Jones authored and Ben Gamari's avatar Ben Gamari committed
      This patch began as a modest refactoring of HsType and friends, to
      clarify and tidy up exactly where quantification takes place in types.
      Although initially driven by making the implementation of wildcards more
      tidy (and fixing a number of bugs), I gradually got drawn into a pretty
      big process, which I've been doing on and off for quite a long time.
      
      There is one compiler performance regression as a result of all
      this, in perf/compiler/T3064.  I still need to look into that.
      
      * The principal driving change is described in Note [HsType binders]
        in HsType.  Well worth reading!
      
      * Those data type changes drive almost everything else.  In particular
        we now statically know where
      
             (a) implicit quantification only (LHsSigType),
                 e.g. in instance declaratios and SPECIALISE signatures
      
             (b) implicit quantification and wildcards (LHsSigWcType)
                 can appear, e.g. in function type signatures
      
      * As part of this change, HsForAllTy is (a) simplified (no...
      1e041b73
  19. 29 Nov, 2015 1 commit
    • quchen's avatar
      Implement warnings for Semigroups as parent of Monoid · 290def72
      quchen authored and Ben Gamari's avatar Ben Gamari committed
      This patch is similar to the AMP patch (#8004), which offered two
      functions:
      
        1. Warn when an instance of a class has been given, but the type does
           not have a certain superclass instance
        2. Warn when top-level definitions conflict with future Prelude names
      
      These warnings are issued as part of the new `-Wcompat` warning group.
      
      Reviewers: hvr, ekmett, austin, bgamari
      
      Reviewed By: hvr, ekmett, bgamari
      
      Subscribers: ekmett, thomie
      
      Differential Revision: https://phabricator.haskell.org/D1539
      
      GHC Trac Issues: #11139
      290def72
  20. 24 Nov, 2015 1 commit
  21. 17 Nov, 2015 2 commits
  22. 16 Nov, 2015 1 commit
  23. 12 Nov, 2015 1 commit
  24. 11 Nov, 2015 1 commit
  25. 31 Oct, 2015 1 commit
  26. 30 Oct, 2015 1 commit
    • Ben Gamari's avatar
      Generate Typeable info at definition sites · 91c6b1f5
      Ben Gamari authored and Ben Gamari's avatar Ben Gamari committed
      This is the second attempt at merging D757.
      
      This patch implements the idea floated in Trac #9858, namely that we
      should generate type-representation information at the data type
      declaration site, rather than when solving a Typeable constraint.
      
      However, this turned out quite a bit harder than I expected. I still
      think it's the right thing to do, and it's done now, but it was quite
      a struggle.
      
      See particularly
      
       * Note [Grand plan for Typeable] in TcTypeable (which is a new module)
       * Note [The overall promotion story] in DataCon (clarifies existing
      stuff)
      
      The most painful bit was that to generate Typeable instances (ie
      TyConRepName bindings) for every TyCon is tricky for types in ghc-prim
      etc:
      
       * We need to have enough data types around to *define* a TyCon
       * Many of these types are wired-in
      
      Also, to minimise the code generated for each data type, I wanted to
      generate pure data, not CAFs with unpackCString# stuff floating about.
      
      Performance
      ~~~~~~~~~~~
      Thre...
      91c6b1f5
  27. 29 Oct, 2015 3 commits
    • Ben Gamari's avatar
      Revert "Generate Typeable info at definition sites" · bbaf76f9
      Ben Gamari authored
      This reverts commit bef2f03e.
      
      This merge was botched
      
      Also reverts haddock submodule.
      bbaf76f9
    • Ben Gamari's avatar
      Generate Typeable info at definition sites · bef2f03e
      Ben Gamari authored
      This patch implements the idea floated in Trac #9858, namely that we
      should generate type-representation information at the data type
      declaration site, rather than when solving a Typeable constraint.
      
      However, this turned out quite a bit harder than I expected. I still
      think it's the right thing to do, and it's done now, but it was quite
      a struggle.
      
      See particularly
      
       * Note [Grand plan for Typeable] in TcTypeable (which is a new module)
       * Note [The overall promotion story] in DataCon (clarifies existing stuff)
      
      The most painful bit was that to generate Typeable instances (ie
      TyConRepName bindings) for every TyCon is tricky for types in ghc-prim
      etc:
      
       * We need to have enough data types around to *define* a TyCon
       * Many of these types are wired-in
      
      Also, to minimise the code generated for each data type, I wanted to
      generate pure data, not CAFs with unpackCString# stuff floating about.
      
      Performance
      ~~~~~~~~~~~
      Three perf/compiler tests start to allocate quite a bit more. This isn't
      surprising, because they all allocate zillions of data types, with
      practically no other code, esp. T1969
      
       * T3294:   GHC allocates 110% more (filed #11030 to track this)
       * T1969:   GHC allocates 30% more
       * T4801:   GHC allocates 14% more
       * T5321FD: GHC allocates 13% more
       * T783:    GHC allocates 12% more
       * T9675:   GHC allocates 12% more
       * T5642:   GHC allocates 10% more
       * T9961:   GHC allocates 6% more
      
       * T9203:   Program allocates 54% less
      
      I'm treating this as acceptable. The payoff comes in Typeable-heavy
      code.
      
      Remaining to do
      ~~~~~~~~~~~~~~~
      
       * I think that "TyCon" and "Module" are over-generic names to use for
         the runtime type representations used in GHC.Typeable. Better might be
         "TrTyCon" and "TrModule". But I have not yet done this
      
       * Add more info the the "TyCon" e.g. source location where it was
         defined
      
       * Use the new "Module" type to help with Trac Trac #10068
      
       * It would be possible to generate TyConRepName (ie Typeable
         instances) selectively rather than all the time. We'd need to persist
         the information in interface files. Lacking a motivating reason I have
         not done this, but it would not be difficult.
      
      Refactoring
      ~~~~~~~~~~~
      As is so often the case, I ended up refactoring more than I intended.
      In particular
      
       * In TyCon, a type *family* (whether type or data) is repesented by a
         FamilyTyCon
           * a algebraic data type (including data/newtype instances) is
             represented by AlgTyCon This wasn't true before; a data family
             was represented as an AlgTyCon. There are some corresponding
             changes in IfaceSyn.
      
           * Also get rid of the (unhelpfully named) tyConParent.
      
       * In TyCon define 'Promoted', isomorphic to Maybe, used when things are
         optionally promoted; and use it elsewhere in GHC.
      
       * Cleanup handling of knownKeyNames
      
       * Each TyCon, including promoted TyCons, contains its TyConRepName, if
         it has one. This is, in effect, the name of its Typeable instance.
      
      Requires update of the haddock submodule.
      
      Differential Revision: https://phabricator.haskell.org/D757
      bef2f03e
    • Matthew Pickering's avatar
      Record pattern synonyms · 2a74a64e
      Matthew Pickering authored and Ben Gamari's avatar Ben Gamari committed
      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 la...
      2a74a64e
  28. 27 Oct, 2015 1 commit
    • Ben Gamari's avatar
      PrelNames: Fix duplicate unique · d1ab6fc9
      Ben Gamari authored
      Previously unboundKey and fromIntegerClassOpKey were sharing a Unique
      Reassign unboundKey to `mkPreludeMiscIdUnique 158`
      d1ab6fc9