1. 01 Mar, 2019 1 commit
    • Ryan Scott's avatar
      Visible dependent quantification · c26d299d
      Ryan Scott authored
      This implements GHC proposal 35
      (https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0035-forall-arrow.rst)
      by adding the ability to write kinds with
      visible dependent quantification (VDQ).
      
      Most of the work for supporting VDQ was actually done _before_ this
      patch. That is, GHC has been able to reason about kinds with VDQ for
      some time, but it lacked the ability to let programmers directly
      write these kinds in the source syntax. This patch is primarly about
      exposing this ability, by:
      
      * Changing `HsForAllTy` to add an additional field of type
        `ForallVisFlag` to distinguish between invisible `forall`s (i.e,
        with dots) and visible `forall`s (i.e., with arrows)
      * Changing `Parser.y` accordingly
      
      The rest of the patch mostly concerns adding validity checking to
      ensure that VDQ is never used in the type of a term (as permitting
      this would require full-spectrum dependent types). This is
      accomplished by:
      
      * Adding a `vdqAllowed` predicate to `TcValidity`.
      * Introducing `splitLHsSigmaTyInvis`, a variant of `splitLHsSigmaTy`
        that only splits invisible `forall`s. This function is used in
        certain places (e.g., in instance declarations) to ensure that GHC
        doesn't try to split visible `forall`s (e.g., if it tried splitting
        `instance forall a -> Show (Blah a)`, then GHC would mistakenly
        allow that declaration!)
      
      This also updates Template Haskell by introducing a new `ForallVisT`
      constructor to `Type`.
      
      Fixes #16326. Also fixes #15658 by documenting this feature in the
      users' guide.
      c26d299d
  2. 24 Feb, 2019 1 commit
    • Simon Peyton Jones's avatar
      Add AnonArgFlag to FunTy · 6cce36f8
      Simon Peyton Jones authored
      The big payload of this patch is:
      
        Add an AnonArgFlag to the FunTy constructor
        of Type, so that
          (FunTy VisArg   t1 t2) means (t1 -> t2)
          (FunTy InvisArg t1 t2) means (t1 => t2)
      
      The big payoff is that we have a simple, local test to make
      when decomposing a type, leading to many fewer calls to
      isPredTy. To me the code seems a lot tidier, and probably
      more efficient (isPredTy has to take the kind of the type).
      
      See Note [Function types] in TyCoRep.
      
      There are lots of consequences
      
      * I made FunTy into a record, so that it'll be easier
        when we add a linearity field, something that is coming
        down the road.
      
      * Lots of code gets touched in a routine way, simply because it
        pattern matches on FunTy.
      
      * I wanted to make a pattern synonym for (FunTy2 arg res), which
        picks out just the argument and result type from the record. But
        alas the pattern-match overlap checker has a heart attack, and
        either reports false positives, or takes too long.  In the end
        I gave up on pattern synonyms.
      
        There's some commented-out code in TyCoRep that shows what I
        wanted to do.
      
      * Much more clarity about predicate types, constraint types
        and (in particular) equality constraints in kinds.  See TyCoRep
        Note [Types for coercions, predicates, and evidence]
        and Note [Constraints in kinds].
      
        This made me realise that we need an AnonArgFlag on
        AnonTCB in a TyConBinder, something that was really plain
        wrong before. See TyCon Note [AnonTCB InivsArg]
      
      * When building function types we must know whether we
        need VisArg (mkVisFunTy) or InvisArg (mkInvisFunTy).
        This turned out to be pretty easy in practice.
      
      * Pretty-printing of types, esp in IfaceType, gets
        tidier, because we were already recording the (->)
        vs (=>) distinction in an ad-hoc way.  Death to
        IfaceFunTy.
      
      * mkLamType needs to keep track of whether it is building
        (t1 -> t2) or (t1 => t2).  See Type
        Note [mkLamType: dictionary arguments]
      
      Other minor stuff
      
      * Some tidy-up in validity checking involving constraints;
        Trac #16263
      6cce36f8
  3. 20 Dec, 2018 1 commit
    • Simon Peyton Jones's avatar
      Refine the suppression of RuntimeRep variables · 5f2a8793
      Simon Peyton Jones authored
      When we pretty-print types, we suppress RuntimeRep variables, but
      we were being too aggressive in doing so, resulting in Trac #16074.
      
      This patch makes the suppression a bit less aggressive.
      See Note [Defaulting RuntimeRep variables]
      5f2a8793
  4. 19 Dec, 2018 1 commit
    • Ryan Scott's avatar
      Fix #16030 by refactoring IfaceSyn's treatment of GADT constructors · 9d9e3557
      Ryan Scott authored
      Summary:
      GHCi's `:info` command was pretty-printined GADT
      constructors suboptimally in the following ways:
      
      1. Sometimes, fields were parenthesized when they did not need it,
         e.g.,
      
      ```lang=haskell
      data Foo a where
        MkFoo :: (Maybe a) -> Foo a
      ```
      
         I fixed this by refactoring some code in `pprIfaceConDecl` to be a
         little smarter with respect to GADT syntax. See `pprFieldArgTy`
         and `pprArgTy`.
      2. With `-fprint-explicit-kinds` enabled, there would be times when
         specified arguments would be printed without a leading `@` in GADT
         return types, e.g.,
      
      ```lang=haskell
      data Bar @k (a :: k) where
        MkBar :: Bar k a
      ```
      
         It turns out that `ppr_tc_app`, the function which pretty-prints
         these return types, was not using the proper machinery to print
         out the arguments, which caused the visibilities to be forgotten
         entirely. I refactored `ppr_tc_app` to do this correctly.
      
      Test Plan: make test TEST=T16030
      
      Reviewers: goldfire, bgamari, simonpj
      
      Reviewed By: simonpj
      
      Subscribers: simonpj, rwbarton, carter
      
      GHC Trac Issues: #16030
      
      Differential Revision: https://phabricator.haskell.org/D5440
      9d9e3557
  5. 03 Dec, 2018 1 commit
  6. 26 Nov, 2018 2 commits
    • Ryan Scott's avatar
      Fix #15941 by only special-casing visible infix applications · 984b75de
      Ryan Scott authored
      Summary:
      The iface pretty-printer had a special case for an
      application of an infix type constructor to two arguments. But this
      didn't take the visibilities of the arguments into account, which
      could lead to strange output like `@{LiftedRep} -> @{LiftedRep}` when
      `-fprint-explicit-kinds` was enabled (#15941). The fix is relatively
      straightforward: simply plumb through the visibilities of each
      argument, and only trigger the special case for infix applications
      if both arguments are visible (i.e., required).
      
      Test Plan: make test TEST=T15941
      
      Reviewers: goldfire, bgamari, monoidal
      
      Reviewed By: goldfire, monoidal
      
      Subscribers: simonpj, rwbarton, carter
      
      GHC Trac Issues: #15941
      
      Differential Revision: https://phabricator.haskell.org/D5375
      984b75de
    • Ryan Scott's avatar
      Print explicit foralls in type family eqns when appropriate · f932b1aa
      Ryan Scott authored
      Summary:
      When `-fprint-explicit-foralls` is enabled, type family
      equations are either printed without an explict `forall` entirely,
      or with a bizarre square bracket syntax (in the case of closed type
      families). I find neither satisfying, so in this patch, I introduce
      support for printing explicit `forall`s in open type-family, closed
      type-family, and data-family equations when appropriate. (By "when
      appropriate", I refer to the conditions laid out in
      `Note [When to print foralls]` in `IfaceType`.)
      
      One tricky point in the implementation is that I had to pick a
      visibility for each type variable in a `CoAxiom`/`FamInst` in order
      to be able to pass it to `pprUserIfaceForAll` //et al.// Because
      the type variables in a type family instance equation can't be
      instantiated by the programmer anyway, the choice only really matters
      for pretty-printing purposes, so I simply went with good ol'
      trustworthy `Specified`. (This design choice is documented in
      `Note [Printing foralls in type family instances]` in `IfaceType`.)
      
      Test Plan: make test TEST=T15827
      
      Reviewers: goldfire, bgamari, simonpj
      
      Reviewed By: simonpj
      
      Subscribers: simonpj, rwbarton, carter
      
      GHC Trac Issues: #15827
      
      Differential Revision: https://phabricator.haskell.org/D5282
      f932b1aa
  7. 22 Nov, 2018 1 commit
    • Ryan Scott's avatar
      Overhaul -fprint-explicit-kinds to use VKA · f5d20838
      Ryan Scott authored
      This patch changes the behavior of `-fprint-explicit-kinds`
      so that it displays kind argument using visible kind application.
      In other words, the flag now:
      
      1. Prints instantiations of specified variables with `@(...)`.
      2. Prints instantiations of inferred variables with `@{...}`.
      
      In addition, this patch removes the `Use -fprint-explicit-kinds to
      see the kind arguments` error message that often arises when a type
      mismatch occurs due to different kinds. Instead, whenever there is a
      kind mismatch, we now enable the `-fprint-explicit-kinds` flag
      locally to help cue to the programmer where the error lies.
      (See `Note [Kind arguments in error messages]` in `TcErrors`.)
      As a result, these funny `@{...}` things can now appear to the user
      even without turning on the `-fprint-explicit-kinds` flag explicitly,
      so I took the liberty of documenting them in the users' guide.
      
      Test Plan: ./validate
      
      Reviewers: goldfire, simonpj, bgamari
      
      Reviewed By: simonpj
      
      Subscribers: rwbarton, carter
      
      GHC Trac Issues: #15871
      
      Differential Revision: https://phabricator.haskell.org/D5314
      f5d20838
  8. 15 Nov, 2018 1 commit
    • Simon Peyton Jones's avatar
      Smarter HsType pretty-print for promoted datacons · ae2c9b40
      Simon Peyton Jones authored
      Fix Trac #15898, by being smarter about when to print
      a space before a promoted data constructor, in a HsType.
      I had to implement a mildly tiresome function
          HsType.lhsTypeHasLeadingPromotionQuote
      It has multiple cases, of course, but it's very simple.
      
      The patch improves the error-message output in a bunch of
      cases, and (to my surprise) actually fixes a bug in the
      output of T14343 (Trac #14343), thus
      
        -  In the expression: _ :: Proxy '('( 'True,  'False),  'False)
        +  In the expression: _ :: Proxy '( '( 'True, 'False), 'False)
      
      I discovered that there were two copies of the PromotionFlag
      type (a boolean, with helpfully named data cons), one in
      IfaceType and one in HsType.  So I combined into one,
      PromotionFlag, and moved it to BasicTypes.  That's why
      quite a few files are touched, but it's all routine.
      ae2c9b40
  9. 04 Oct, 2018 1 commit
    • Simon Peyton Jones's avatar
      Better pretty-printing of forall types · 37ef7031
      Simon Peyton Jones authored
      Currently forall-types with a lot of type variables,
      or type variables with big kinds, are pretty-printed too
      horizontally, and dribble off to the right in an illegible
      way.
      
      This patch treats the type variables as a group, and uses
      'fsep' to lay them out decently.
      37ef7031
  10. 15 Sep, 2018 1 commit
    • Ningning Xie's avatar
      Coercion Quantification · ea5ade34
      Ningning Xie authored
      This patch corresponds to #15497.
      
      According to https://ghc.haskell.org/trac/ghc/wiki/DependentHaskell/Phase2,
       we would like to have coercion quantifications back. This will
      allow us to migrate (~#) to be homogeneous, instead of its current
      heterogeneous definition. This patch is (lots of) plumbing only. There
      should be no user-visible effects.
      
      An overview of changes:
      
      - Both `ForAllTy` and `ForAllCo` can quantify over coercion variables,
      but only in *Core*. All relevant functions are updated accordingly.
      - Small changes that should be irrelevant to the main task:
          1. removed dead code `mkTransAppCo` in Coercion
          2. removed out-dated Note Computing a coercion kind and
             roles in Coercion
          3. Added `Eq4` in Note Respecting definitional equality in
             TyCoRep, and updated `mkCastTy` accordingly.
          4. Various updates and corrections of notes and typos.
      - Haddock submodule needs to be changed too.
      
      Acknowledgments:
      This work was completed mostly during Ningning Xie's Google Summer
      of Code, sponsored by Google. It was advised by Richard Eisenberg,
      supported by NSF grant 1704041.
      
      Test Plan: ./validate
      
      Reviewers: goldfire, simonpj, bgamari, hvr, erikd, simonmar
      
      Subscribers: RyanGlScott, monoidal, rwbarton, carter
      
      GHC Trac Issues: #15497
      
      Differential Revision: https://phabricator.haskell.org/D5054
      ea5ade34
  11. 24 Aug, 2018 1 commit
  12. 05 Aug, 2018 1 commit
  13. 11 Jul, 2018 1 commit
    • Ryan Scott's avatar
      Use IfaceAppArgs to store an IfaceAppTy's arguments · 1c353623
      Ryan Scott authored
      Summary:
      Currently, an `IfaceAppTy` has no way to tell whether its
      argument is visible or not, so it simply treats all arguments as
      visible, leading to #15330. We already have a solution for this
      problem in the form of the `IfaceTcArgs` data structure, used by
      `IfaceTyConApp` to represent the arguments to a type constructor.
      Therefore, it makes sense to reuse this machinery for `IfaceAppTy`,
      so this patch does just that.
      
      This patch:
      
      1. Renames `IfaceTcArgs` to `IfaceAppArgs` to reflect its more
         general purpose.
      2. Changes the second field of `IfaceAppTy` from `IfaceType` to
         `IfaceAppArgs`, and propagates the necessary changes through. In
         particular, pretty-printing an `IfaceAppTy` now goes through the
         `IfaceAppArgs` pretty-printer, which correctly displays arguments
         as visible or not for free, fixing #15330.
      3. Changes `toIfaceTypeX` and related functions so that when
         converting an `AppTy` to an `IfaceAppTy`, it flattens as many
         argument `AppTy`s as possible, and then converts those arguments
         into an `IfaceAppArgs` list, using the kind of the function
         `Type` as a guide. (Doing so minimizes the number of times we need
         to call `typeKind`, which is more expensive that finding the kind
         of a `TyCon`.)
      
      Test Plan: make test TEST=T15330
      
      Reviewers: goldfire, simonpj, bgamari
      
      Reviewed By: simonpj
      
      Subscribers: rwbarton, thomie, carter
      
      GHC Trac Issues: #15330
      
      Differential Revision: https://phabricator.haskell.org/D4938
      1c353623
  14. 10 Jul, 2018 1 commit
    • Ningning Xie's avatar
      Refactor coercion rule · 55a3f855
      Ningning Xie authored
      Summary:
      The patch is an attempt on #15192.
      
      It defines a new coercion rule
      
      ```
       | GRefl Role Type MCoercion
      ```
      
      which correspondes to the typing rule
      
      ```
           t1 : k1
        ------------------------------------
        GRefl r t1 MRefl: t1 ~r t1
      
           t1 : k1       co :: k1 ~ k2
        ------------------------------------
        GRefl r t1 (MCo co) : t1 ~r t1 |> co
      ```
      
      MCoercion wraps a coercion, which might be reflexive (MRefl)
      or not (MCo co). To know more about MCoercion see #14975.
      
      We keep Refl ty as a special case for nominal reflexive coercions,
      naemly, Refl ty :: ty ~n ty.
      
      This commit is meant to be a general performance improvement,
      but there are a few regressions. See #15192, comment:13 for
      more information.
      
      Test Plan: ./validate
      
      Reviewers: bgamari, goldfire, simonpj
      
      Subscribers: rwbarton, thomie, carter
      
      GHC Trac Issues: #15192
      
      Differential Revision: https://phabricator.haskell.org/D4747
      55a3f855
  15. 05 Jul, 2018 2 commits
    • Ryan Scott's avatar
      Make ppr_tc_args aware of -fprint-explicit-kinds · dbdcacfc
      Ryan Scott authored
      Summary:
      `ppr_tc_args` was printing invisible kind arguments even
      when `-fprint-explicit-kinds` wasn't enabled. Easily fixed.
      
      Test Plan: make test TEST=T15341
      
      Reviewers: goldfire, bgamari, simonpj
      
      Reviewed By: simonpj
      
      Subscribers: simonpj, rwbarton, thomie, carter
      
      GHC Trac Issues: #15341
      
      Differential Revision: https://phabricator.haskell.org/D4932
      dbdcacfc
    • Ryan Scott's avatar
      Fix #15308 by suppressing invisble args more rigorously · 93b7ac8d
      Ryan Scott authored
      Summary:
      There was a buglet in `stripInvisArgs` (which is part of the
      pretty-printing pipeline for types) in which only invisble arguments
      which came before any visible arguments would be suppressed, but any
      invisble arguments that came //after// visible ones would still be
      printed, even if `-fprint-explicit-kinds`  wasn't enabled.
      The fix is simple: make `stripInvisArgs` recursively process the
      remaining types even after a visible argument is encountered.
      
      Test Plan: make test TEST=T15308
      
      Reviewers: goldfire, bgamari
      
      Reviewed By: bgamari
      
      Subscribers: simonpj, rwbarton, thomie, carter
      
      GHC Trac Issues: #15308
      
      Differential Revision: https://phabricator.haskell.org/D4891
      93b7ac8d
  16. 14 Jun, 2018 1 commit
    • Vladislav Zavialov's avatar
      Embrace -XTypeInType, add -XStarIsType · d650729f
      Vladislav Zavialov authored
      Summary:
      Implement the "Embrace Type :: Type" GHC proposal,
      .../ghc-proposals/blob/master/proposals/0020-no-type-in-type.rst
      
      GHC 8.0 included a major change to GHC's type system: the Type :: Type
      axiom. Though casual users were protected from this by hiding its
      features behind the -XTypeInType extension, all programs written in GHC
      8+ have the axiom behind the scenes. In order to preserve backward
      compatibility, various legacy features were left unchanged. For example,
      with -XDataKinds but not -XTypeInType, GADTs could not be used in types.
      Now these restrictions are lifted and -XTypeInType becomes a redundant
      flag that will be eventually deprecated.
      
      * Incorporate the features currently in -XTypeInType into the
        -XPolyKinds and -XDataKinds extensions.
      * Introduce a new extension -XStarIsType to control how to parse * in
        code and whether to print it in error messages.
      
      Test Plan: Validate
      
      Reviewers: goldfire, hvr, bgamari, alanz, simonpj
      
      Reviewed By: goldfire, simonpj
      
      Subscribers: rwbarton, thomie, mpickering, carter
      
      GHC Trac Issues: #15195
      
      Differential Revision: https://phabricator.haskell.org/D4748
      d650729f
  17. 08 Jun, 2018 1 commit
  18. 07 Jun, 2018 1 commit
    • Andreas Herrmann's avatar
      Fix unparseable pretty-printing of promoted data cons · 767536cc
      Andreas Herrmann authored
      Previously we would print code which would not round-trip:
      ```
      > :set -XDataKinds
      > :set -XPolyKinds
      > data Proxy k = Proxy
      > _ :: Proxy '[ 'True ]
      error:
        Found hole: _ :: Proxy '['True]
      > _ :: Proxy '['True]
      error:
          Invalid type signature: _ :: ...
          Should be of form <variable> :: <type>
      ```
      
      Test Plan: Validate with T14343
      
      Reviewers: RyanGlScott, goldfire, bgamari, tdammers
      
      Reviewed By: RyanGlScott, bgamari
      
      Subscribers: tdammers, rwbarton, thomie, carter
      
      GHC Trac Issues: #14343
      
      Differential Revision: https://phabricator.haskell.org/D4746
      767536cc
  19. 02 Jun, 2018 1 commit
    • Ben Gamari's avatar
      vectorise: Put it out of its misery · faee23bb
      Ben Gamari authored
      Poor DPH and its vectoriser have long been languishing; sadly it seems there is
      little chance that the effort will be rekindled. Every few years we discuss
      what to do with this mass of code and at least once we have agreed that it
      should be archived on a branch and removed from `master`. Here we do just that,
      eliminating heaps of dead code in the process.
      
      Here we drop the ParallelArrays extension, the vectoriser, and the `vector` and
      `primitive` submodules.
      
      Test Plan: Validate
      
      Reviewers: simonpj, simonmar, hvr, goldfire, alanz
      
      Reviewed By: simonmar
      
      Subscribers: goldfire, rwbarton, thomie, mpickering, carter
      
      Differential Revision: https://phabricator.haskell.org/D4761
      faee23bb
  20. 16 May, 2018 1 commit
    • Ryan Scott's avatar
      Fix #15039 by pretty-printing equalities more systematically · 99f8cc84
      Ryan Scott authored
      GHC previously had a handful of special cases for
      pretty-printing equalities in a more user-friendly manner, but they
      were far from comprehensive (see #15039 for an example of where this
      fell apart).
      
      This patch makes the pretty-printing of equalities much more
      systematic. I've adopted the approach laid out in
      https://ghc.haskell.org/trac/ghc/ticket/15039#comment:4, and updated
      `Note [Equality predicates in IfaceType]` accordingly. We are now
      more careful to respect the properties of the
      `-fprint-explicit-kinds` and `-fprint-equality-relations` flags,
      which led to some improvements in error message outputs.
      
      Along the way, I also tweaked the error-reporting machinery not to
      print out the type of a typed hole when the type is an unlifted
      equality, since it's kind (`TYPE ('TupleRep '[])`) was more
      confusing than anything.
      
      Test Plan: make test TEST="T15039a T15039b T15039c T15039d"
      
      Reviewers: simonpj, goldfire, bgamari
      
      Reviewed By: simonpj
      
      Subscribers: rwbarton, thomie, carter
      
      GHC Trac Issues: #15039
      
      Differential Revision: https://phabricator.haskell.org/D4696
      99f8cc84
  21. 14 May, 2018 1 commit
    • Ryan Scott's avatar
      Fix #14875 by introducing PprPrec, and using it · 21e1a00c
      Ryan Scott authored
      Trying to determine when to insert parentheses during TH
      conversion is a bit of a mess. There is an assortment of functions
      that try to detect this, such as:
      
      * `hsExprNeedsParens`
      * `isCompoundHsType`
      * `hsPatNeedsParens`
      * `isCompoundPat`
      * etc.
      
      To make things worse, each of them have slightly different semantics.
      Plus, they don't work well in the presence of explicit type
      signatures, as #14875 demonstrates.
      
      All of these problems can be alleviated with the use of an explicit
      precedence argument (much like what `showsPrec` currently does). To
      accomplish this, I introduce a new `PprPrec` data type, and define
      standard predences for things like function application, infix
      operators, function arrows, and explicit type signatures (that last
      one is new). I then added `PprPrec` arguments to the various
      `-NeedsParens` functions, and use them to make smarter decisions
      about when things need to be parenthesized.
      
      A nice side effect is that functions like `isCompoundHsType` are
      now completely unneeded, since they're simply aliases for
      `hsTypeNeedsParens appPrec`. As a result, I did a bit of refactoring
      to remove these sorts of functions. I also did a pass over various
      utility functions in GHC for constructing AST forms and used more
      appropriate precedences where convenient.
      
      Along the way, I also ripped out the existing `TyPrec`
      data type (which was tailor-made for pretty-printing `Type`s) and
      replaced it with `PprPrec` for consistency.
      
      Test Plan: make test TEST=T14875
      
      Reviewers: alanz, goldfire, bgamari
      
      Reviewed By: bgamari
      
      Subscribers: rwbarton, thomie, carter
      
      GHC Trac Issues: #14875
      
      Differential Revision: https://phabricator.haskell.org/D4688
      21e1a00c
  22. 07 Apr, 2018 1 commit
    • Ryan Scott's avatar
      Fix #14238 by always pretty-printing visible tyvars · 718a0181
      Ryan Scott authored
      Summary:
      Before, GHC would never print visible tyvars in the absence
      of `-fprint-explicit-foralls`, which led to `:kind` displaying
      incorrect kinds in GHCi. The fix is simple—simply check beforehand
      if any of the type variable binders are required when deciding when
      to pretty-print them.
      
      Test Plan: make test TEST=T14238
      
      Reviewers: simonpj, goldfire, bgamari
      
      Subscribers: thomie, carter
      
      GHC Trac Issues: #14238
      
      Differential Revision: https://phabricator.haskell.org/D4564
      718a0181
  23. 01 Apr, 2018 1 commit
    • Richard Eisenberg's avatar
      Track type variable scope more carefully. · faec8d35
      Richard Eisenberg authored
      The main job of this commit is to track more accurately the scope
      of tyvars introduced by user-written foralls. For example, it would
      be to have something like this:
      
        forall a. Int -> (forall k (b :: k). Proxy '[a, b]) -> Bool
      
      In that type, a's kind must be k, but k isn't in scope. We had a
      terrible way of doing this before (not worth repeating or describing
      here, but see the old tcImplicitTKBndrs and friends), but now
      we have a principled approach: make an Implication when kind-checking
      a forall. Doing so then hooks into the existing machinery for
      preventing skolem-escape, performing floating, etc. This also means
      that we bump the TcLevel whenever going into a forall.
      
      The new behavior is done in TcHsType.scopeTyVars, but see also
      TcHsType.tc{Im,Ex}plicitTKBndrs, which have undergone significant
      rewriting. There are several Notes near there to guide you. Of
      particular interest there is that Implication constraints can now
      have skolems that are out of order; this situation is reported in
      TcErrors.
      
      A major consequence of this is a slightly tweaked process for type-
      checking type declarations. The new Note [Use SigTvs in kind-checking
      pass] in TcTyClsDecls lays it out.
      
      The error message for dependent/should_fail/TypeSkolEscape has become
      noticeably worse. However, this is because the code in TcErrors goes to
      some length to preserve pre-8.0 error messages for kind errors. It's time
      to rip off that plaster and get rid of much of the kind-error-specific
      error messages. I tried this, and doing so led to a lovely error message
      for TypeSkolEscape. So: I'm accepting the error message quality regression
      for now, but will open up a new ticket to fix it, along with a larger
      error-message improvement I've been pondering. This applies also to
      dependent/should_fail/{BadTelescope2,T14066,T14066e}, polykinds/T11142.
      
      Other minor changes:
       - isUnliftedTypeKind didn't look for tuples and sums. It does now.
      
       - check_type used check_arg_type on both sides of an AppTy. But the left
         side of an AppTy isn't an arg, and this was causing a bad error message.
         I've changed it to use check_type on the left-hand side.
      
       - Some refactoring around when we print (TYPE blah) in error messages.
         The changes decrease the times when we do so, to good effect.
         Of course, this is still all controlled by
         -fprint-explicit-runtime-reps
      
      Fixes #14066 #14749
      
      Test cases: dependent/should_compile/{T14066a,T14749},
                  dependent/should_fail/T14066{,c,d,e,f,g,h}
      faec8d35
  24. 19 Mar, 2018 1 commit
  25. 03 Mar, 2018 1 commit
    • Ryan Scott's avatar
      Parenthesize (() :: Constraint) in argument position · 99c556d2
      Ryan Scott authored
      Summary:
      A simple oversight in the pretty-printer lead to a special
      case for `() :: Constraint` not being parenthesized correctly when
      used in an argument position. Easily fixed with a `maybeParen`.
      
      Test Plan: make test TEST=T14796
      
      Reviewers: alanz, goldfire, bgamari, simonpj
      
      Reviewed By: bgamari, simonpj
      
      Subscribers: simonpj, rwbarton, thomie, carter
      
      GHC Trac Issues: #14796
      
      Differential Revision: https://phabricator.haskell.org/D4408
      99c556d2
  26. 03 Jan, 2018 1 commit
  27. 21 Dec, 2017 1 commit
    • Simon Peyton Jones's avatar
      Refactor coercion holes · a492af06
      Simon Peyton Jones authored
      In fixing Trac #14584 I found that it would be /much/ more
      convenient if a "hole" in a coercion (much like a unification
      variable in a type) acutally had a CoVar associated with it
      rather than just a Unique.  Then I can ask what the free variables
      of a coercion is, and get a set of CoVars including those
      as-yet-un-filled in holes.
      
      Once that is done, it makes no sense to stuff coercion holes
      inside UnivCo.  They were there before so we could know the
      kind and role of a "hole" coercion, but once there is a CoVar
      we can get that info from the CoVar.  So I removed HoleProv
      from UnivCoProvenance and added HoleCo to Coercion.
      
      In summary:
      
      * Add HoleCo to Coercion and remove HoleProv from UnivCoProvanance
      
      * Similarly in IfaceCoercion
      
      * Make CoercionHole have a CoVar in it, not a Unique
      
      * Make tyCoVarsOfCo return the free coercion-hole variables
        as well as the ordinary free CoVars.  Similarly, remember
        to zonk the CoVar in a CoercionHole
      
      We could go further, and remove CoercionHole as a distinct type
      altogther, just collapsing it into HoleCo.  But I have not done
      that yet.
      a492af06
  28. 31 Oct, 2017 1 commit
    • Simon Peyton Jones's avatar
      Tidy up IfaceEqualityTyCon · 29ae8337
      Simon Peyton Jones authored
      This commit
      
        commit 85aa1f42
        Date:   Sun Oct 29 20:48:19 2017 -0400
          Fix #14390 by making toIfaceTyCon aware of equality
      
      was a bit over-complicated. This patch simplifies the (horribly
      ad-hoc) treatement of IfaceEqualityTyCon, and documents it better.
      
      No visible change in behaviour.
      29ae8337
  29. 03 Oct, 2017 1 commit
    • Ryan Scott's avatar
      Track the order of user-written tyvars in DataCon · ef26182e
      Ryan Scott authored
      After typechecking a data constructor's type signature, its type
      variables are partitioned into two distinct groups: the universally
      quantified type variables and the existentially quantified type
      variables. Then, when prompted for the type of the data constructor,
      GHC gives this:
      
      ```lang=haskell
      MkT :: forall <univs> <exis>. (...)
      ```
      
      For H98-style datatypes, this is a fine thing to do. But for GADTs,
      this can sometimes produce undesired results with respect to
      `TypeApplications`. For instance, consider this datatype:
      
      ```lang=haskell
      data T a where
        MkT :: forall b a. b -> T a
      ```
      
      Here, the user clearly intended to have `b` be available for visible
      type application before `a`. That is, the user would expect
      `MkT @Int @Char` to be of type `Int -> T Char`, //not//
      `Char -> T Int`. But alas, up until now that was not how GHC
      operated—regardless of the order in which the user actually wrote
      the tyvars, GHC would give `MkT` the type:
      
      ```lang=haskell
      MkT :: forall a b. b -> T a
      ```
      
      Since `a` is universal and `b` is existential. This makes predicting
      what order to use for `TypeApplications` quite annoying, as
      demonstrated in #11721 and #13848.
      
      This patch cures the problem by tracking more carefully the order in
      which a user writes type variables in data constructor type
      signatures, either explicitly (with a `forall`) or implicitly
      (without a `forall`, in which case the order is inferred). This is
      accomplished by adding a new field `dcUserTyVars` to `DataCon`, which
      is a subset of `dcUnivTyVars` and `dcExTyVars` that is permuted to
      the order in which the user wrote them. For more details, refer to
      `Note [DataCon user type variables]` in `DataCon.hs`.
      
      An interesting consequence of this design is that more data
      constructors require wrappers. This is because the workers always
      expect the first arguments to be the universal tyvars followed by the
      existential tyvars, so when the user writes the tyvars in a different
      order, a wrapper type is needed to swizzle the tyvars around to match
      the order that the worker expects. For more details, refer to
      `Note [Data con wrappers and GADT syntax]` in `MkId.hs`.
      
      Test Plan: ./validate
      
      Reviewers: austin, goldfire, bgamari, simonpj
      
      Reviewed By: goldfire, simonpj
      
      Subscribers: ezyang, goldfire, rwbarton, thomie
      
      GHC Trac Issues: #11721, #13848
      
      Differential Revision: https://phabricator.haskell.org/D3687
      ef26182e
  30. 19 Sep, 2017 1 commit
    • Herbert Valerio Riedel's avatar
      compiler: introduce custom "GhcPrelude" Prelude · f63bc730
      Herbert Valerio Riedel authored
      This switches the compiler/ component to get compiled with
      -XNoImplicitPrelude and a `import GhcPrelude` is inserted in all
      modules.
      
      This is motivated by the upcoming "Prelude" re-export of
      `Semigroup((<>))` which would cause lots of name clashes in every
      modulewhich imports also `Outputable`
      
      Reviewers: austin, goldfire, bgamari, alanz, simonmar
      
      Reviewed By: bgamari
      
      Subscribers: goldfire, rwbarton, thomie, mpickering, bgamari
      
      Differential Revision: https://phabricator.haskell.org/D3989
      f63bc730
  31. 14 Sep, 2017 2 commits
    • Richard Eisenberg's avatar
      Fix #13963. · 8f99cd67
      Richard Eisenberg authored
      This commit fixes several things:
      
      1. RuntimeRep arg suppression was overeager for *visibly*-quantified
      RuntimeReps, which should remain.
      
      2. The choice of whether to used a Named TyConBinder or an anonymous
      was sometimes wrong. Now, we do an extra little pass right before
      constructing the tycon to fix these.
      
      3. TyCons that normally cannot appear unsaturated can appear unsaturated
      in :kind. But this fact was not propagated into the type checker.
      It now is.
      8f99cd67
    • Richard Eisenberg's avatar
      Fix #13407 by suppressing invisibles better. · 04bb8736
      Richard Eisenberg authored
      Previously, the iface-invisible-suppresser assumed that all
      invisible things are up front. Not true!
      
      test case: ghci/scripts/T13407
      04bb8736
  32. 02 Sep, 2017 1 commit
    • Ryan Scott's avatar
      Fix #14167 by using isGadtSyntaxTyCon in more places · 8e4229ab
      Ryan Scott authored
      Summary:
      Two places in GHC effectively attempt to //guess// whether a data type
      was declared using GADT syntax:
      
      1. When reifying a data type in Template Haskell
      2. When pretty-printing a data type (e.g., via `:info` in GHCi)
      
      But there's no need for heuristics here, since we have a 100% accurate way to
      determine whether a data type was declared using GADT syntax: the
      `isGadtSyntaxTyCon` function! By simply using that as the metric, we obtain
      far more accurate TH reification and pretty-printing results.
      
      This is technically a breaking change, since Template Haskell reification will
      now reify some data type constructors as `(Rec)GadtC` that it didn't before,
      and some data type constructors that were previously reified as `(Rec)GadtC`
      will no longer be reified as such. But it's a very understandable breaking
      change, since the previous behavior was simply incorrect.
      
      Test Plan: ./validate
      
      Reviewers: simonpj, goldfire, austin, bgamari
      
      Reviewed By: simonpj
      
      Subscribers: rwbarton, thomie
      
      GHC Trac Issues: #14167
      
      Differential Revision: https://phabricator.haskell.org/D3901
      8e4229ab
  33. 31 Aug, 2017 2 commits
    • Herbert Valerio Riedel's avatar
      Add missing Semigroup instances to compiler · c0feee90
      Herbert Valerio Riedel authored
      This is a pre-requisite for implementing the Semigroup/Monoid proposal.
      The instances have been introduced in a way to minimise warnings.
      c0feee90
    • Simon Peyton Jones's avatar
      Add debugPprType · 805b29bb
      Simon Peyton Jones authored
      We pretty-print a type by converting it to an IfaceType and
      pretty-printing that.  But
       (a) that's a bit indirect, and
       (b) delibrately loses information about (e.g.) the kind
            on the /occurrences/ of a type variable
      
      So this patch implements debugPprType, which pretty prints
      the type directly, with no fancy formatting.  It's just used
      for debugging.
      
      I took the opportunity to refactor the debug-pretty-printing
      machinery a little.  In particular, define these functions
      and use them:
      
        ifPprDeubug :: SDoc -> SDOc -> SDoc
          -- Says what to do with and without -dppr-debug
        whenPprDebug :: SDoc -> SDoc
          -- Says what to do with  -dppr-debug; without is empty
        getPprDebug :: (Bool -> SDoc) -> SDoc
      
      getPprDebug used to be called sdocPprDebugWith
      whenPprDebug used to be called ifPprDebug
      
      So a lot of files get touched in a very mechanical way
      805b29bb
  34. 27 Jul, 2017 2 commits
  35. 26 May, 2017 1 commit
    • Simon Peyton Jones's avatar
      Some tidying up of type pretty-printing · ad14efd5
      Simon Peyton Jones authored
      Triggered by the changes in #13677, I ended up doing a bit of
      refactoring in type pretty-printing.
      
      * We were using TyOpPrec and FunPrec rather inconsitently, so
        I made it consisent.
      
      * That exposed the fact that we were a bit undecided about whether
        to print
           a + b -> c + d   vs   (a+b) -> (c+d)
        and similarly
           a ~ [b] => blah  vs   (a ~ [b]) => blah
      
        I decided to make TyOpPrec and FunPrec compare equal
        (in BasicTypes), so (->) is treated as equal precedence with
        other type operators, so you get the unambiguous forms above,
        even though they have more parens.
      
        We could readily reverse this decision.
        See Note [Type operator precedence] in BasicTypes
      
      * I fixed a bug in pretty-printing of HsType where some
        parens were omitted by mistake.
      ad14efd5