1. 22 Apr, 2015 1 commit
  2. 23 Mar, 2015 1 commit
    • eir@cis.upenn.edu's avatar
      Do proper depth checking in the flattener to avoid looping. · c1edbdfd
      eir@cis.upenn.edu authored
      This implements (roughly) the plan put forward in comment:14:ticket:7788,
      fixing #7788, #8550, #9554, #10139, and addressing concerns raised in #10079.
      There are some regressions w.r.t. GHC 7.8, but only with pathological type
      families (like F a = F a). This also (hopefully -- don't have a test case)
      fixes #10158. Unsolved problems include #10184 and #10185, which are both
      known deficiencies of the approach used here.
      As part of this change, the plumbing around detecting infinite loops has
      changed. Instead of -fcontext-stack and -ftype-function-depth, we now have
      one combined -freduction-depth parameter. Setting it to 0 disbales the
      check, which is now the recommended way to get (terminating) code to
      typecheck in releases. (The number of reduction steps may well change between
      minor GHC releases!)
      This commit also introduces a new IntWithInf type in BasicTypes
      that represents an integer+infinity. This type is used in a few
      places throughout the code.
      Tests in
        typecheck/should_compile/T10184  (expected broken)
        typecheck/should_compile/T10185  (expected broken)
      This commit also changes performance testsuite numbers, for the better.
  3. 11 Feb, 2015 1 commit
  4. 06 Feb, 2015 1 commit
  5. 19 Dec, 2014 1 commit
  6. 11 Dec, 2014 1 commit
  7. 01 Dec, 2014 1 commit
  8. 04 Nov, 2014 3 commits
  9. 04 Sep, 2014 1 commit
  10. 29 Aug, 2014 1 commit
  11. 28 Aug, 2014 1 commit
  12. 18 Jul, 2014 1 commit
    • Simon Peyton Jones's avatar
      Further improvements to floating equalities · 4b3df0bb
      Simon Peyton Jones authored
      This equality-floating stuff is horribly delicate!  Trac #9316 showed
      up yet another corner case.
      The main changes are
       * include CTyVarEqs when "growing" the skolem set
       * do not include the kind argument to (~) when growing the skolem set
      I added a lot more comments as well
  13. 11 Jun, 2014 1 commit
  14. 10 Apr, 2014 1 commit
    • Simon Peyton Jones's avatar
      Fix egregious blunder in the type flattener · b8132a9d
      Simon Peyton Jones authored
      In tidying up the flattener I introduced an error that no
      regression test caught, giving rise to Trac #8978, #8979.
      It shows up if you have a type synonym whose RHS mentions
      type functions, such sas
           type family F a
           type T a = (F a, a)   -- This synonym isn't properly flattened
      The fix is easy, but sadly the bug is in the released GHC 7.8.1
  15. 24 Mar, 2014 1 commit
    • Simon Peyton Jones's avatar
      Flattener preserves synonyms, rewriteEvidence can drop buggy "optimisation" · 6ae678e3
      Simon Peyton Jones authored
      There was a special case in rewriteEvidence, looking like:
        = return (Just (if ctEvPred old_ev `tcEqType` new_pred
                        then old_ev
                        else old_ev { ctev_pred = new_pred }))
      But this was wrong: old_pred and new_pred might differ in the kind
      of a TyVar occurrence, in which case tcEqType would not notice,
      but we really, really want new_pred.  This caused Trac #8913.
      I solved this by dropping the whole test, and instead making
      the flattener preserve type synonyms. This was easy because
      TcEvidence has TcTyConAppCo which (unlike) Coercion, handles
  16. 17 Mar, 2014 1 commit
  17. 23 Jan, 2014 1 commit
  18. 16 Jan, 2014 1 commit
  19. 10 Jan, 2014 1 commit
  20. 22 Nov, 2013 2 commits
  21. 06 Nov, 2013 1 commit
  22. 05 Aug, 2013 1 commit
  23. 02 Aug, 2013 1 commit
  24. 28 Jun, 2013 1 commit
  25. 25 Jun, 2013 1 commit
  26. 24 Jun, 2013 1 commit
  27. 21 Jun, 2013 1 commit
  28. 30 May, 2013 2 commits
  29. 16 Apr, 2013 1 commit
  30. 03 Apr, 2013 1 commit
  31. 11 Feb, 2013 1 commit
  32. 30 Jan, 2013 1 commit
  33. 16 Jan, 2013 1 commit
  34. 22 Dec, 2012 1 commit
    • eir@cis.upenn.edu's avatar
      Implement overlapping type family instances. · 7a42cf66
      eir@cis.upenn.edu authored
      An ordered, overlapping type family instance is introduced by 'type
      where', followed by equations. See the new section in the user manual
      ( for details. The canonical example is Boolean equality at the
      type family Equals (a :: k) (b :: k) :: Bool
      type instance where
        Equals a a = True
        Equals a b = False
      A branched family instance, such as this one, checks its equations in
      and applies only the first the matches. As explained in the note
      checking within groups] in FamInstEnv.lhs, we must be careful not to
      say, (Equals Int b) to False, because b might later unify with Int.
      This commit includes all of the commits on the overlapping-tyfams
      branch. SPJ
      requested that I combine all my commits over the past several months
      into one
      monolithic commit. The following GHC repos are affected: ghc, testsuite,
      utils/haddock, libraries/template-haskell, and libraries/dph.
      Here are some details for the interested:
      - The definition of CoAxiom has been moved from TyCon.lhs to a
        new file CoAxiom.lhs. I made this decision because of the
        number of definitions necessary to support BranchList.
      - BranchList is a GADT whose type tracks whether it is a
        singleton list or not-necessarily-a-singleton-list. The reason
        I introduced this type is to increase static checking of places
        where GHC code assumes that a FamInst or CoAxiom is indeed a
        singleton. This assumption takes place roughly 10 times
        throughout the code. I was worried that a future change to GHC
        would invalidate the assumption, and GHC might subtly fail to
        do the right thing. By explicitly labeling CoAxioms and
        FamInsts as being Unbranched (singleton) or
        Branched (not-necessarily-singleton), we make this assumption
        explicit and checkable. Furthermore, to enforce the accuracy of
        this label, the list of branches of a CoAxiom or FamInst is
        stored using a BranchList, whose constructors constrain its
        type index appropriately.
      I think that the decision to use BranchList is probably the most
      controversial decision I made from a code design point of view.
      Although I provide conversions to/from ordinary lists, it is more
      efficient to use the brList... functions provided in CoAxiom than
      always to convert. The use of these functions does not wander far
      from the core CoAxiom/FamInst logic.
      BranchLists are motivated and explained in the note [Branched axioms] in
      - The CoAxiom type has changed significantly. You can see the new
        type in CoAxiom.lhs. It uses a CoAxBranch type to track
        branches of the CoAxiom. Correspondingly various functions
        producing and consuming CoAxioms had to change, including the
        binary layout of interface files.
      - To get branched axioms to work correctly, it is important to have a
        of type "apartness": two types are apart if they cannot unify, and no
        substitution of variables can ever get them to unify, even after type
        simplification. (This is different than the normal failure to unify
        of the type family bit.) This notion in encoded in tcApartTys, in
        Because apartness is finer-grained than unification, the tcUnifyTys
        calls tcApartTys.
      - CoreLinting axioms has been updated, both to reflect the new
        form of CoAxiom and to enforce the apartness rules of branch
        application. The formalization of the new rules is in
      - The FamInst type (in types/FamInstEnv.lhs) has changed
        significantly, paralleling the changes to CoAxiom. Of course,
        this forced minor changes in many files.
      - There are several new Notes in FamInstEnv.lhs, including one
        discussing confluent overlap and why we're not doing it.
      - lookupFamInstEnv, lookupFamInstEnvConflicts, and
        lookup_fam_inst_env' (the function that actually does the work)
        have all been more-or-less completely rewritten. There is a
        Note [lookup_fam_inst_env' implementation] describing the
        implementation. One of the changes that affects other files is
        to change the type of matches from a pair of (FamInst, [Type])
        to a new datatype (which now includes the index of the matching
        branch). This seemed a better design.
      - The TySynInstD constructor in Template Haskell was updated to
        use the new datatype TySynEqn. I also bumped the TH version
        number, requiring changes to DPH cabal files. (That's why the
        DPH repo has an overlapping-tyfams branch.)
      - As SPJ requested, I refactored some of the code in HsDecls:
       * splitting up TyDecl into SynDecl and DataDecl, correspondingly
         changing HsTyDefn to HsDataDefn (with only one constructor)
       * splitting FamInstD into TyFamInstD and DataFamInstD and
         splitting FamInstDecl into DataFamInstDecl and TyFamInstDecl
       * making the ClsInstD take a ClsInstDecl, for parallelism with
         InstDecl's other constructors
       * changing constructor TyFamily into FamDecl
       * creating a FamilyDecl type that stores the details for a family
         declaration; this is useful because FamilyDecls can appear in classes
         other decls cannot
       * restricting the associated types and associated type defaults for a
       * class
         to be the new, more restrictive types
       * splitting cid_fam_insts into cid_tyfam_insts and cid_datafam_insts,
         according to the new types
       * perhaps one or two more that I'm overlooking
      None of these changes has far-reaching implications.
      - The user manual, section, is updated to describe the new type
  35. 19 Dec, 2012 1 commit
  36. 08 Dec, 2012 1 commit