• Richard Eisenberg's avatar
    Update levity polymorphism · e7985ed2
    Richard Eisenberg authored
    This commit implements the proposal in
    https://github.com/ghc-proposals/ghc-proposals/pull/29 and
    https://github.com/ghc-proposals/ghc-proposals/pull/35.
    
    Here are some of the pieces of that proposal:
    
    * Some of RuntimeRep's constructors have been shortened.
    
    * TupleRep and SumRep are now parameterized over a list of RuntimeReps.
    * This
    means that two types with the same kind surely have the same
    representation.
    Previously, all unboxed tuples had the same kind, and thus the fact
    above was
    false.
    
    * RepType.typePrimRep and friends now return a *list* of PrimReps. These
    functions can now work successfully on unboxed tuples. This change is
    necessary because we allow abstraction over unboxed tuple types and so
    cannot
    always handle unboxed tuples specially as we did before.
    
    * We sometimes have to create an Id from a PrimRep. I thus split PtrRep
    * into
    LiftedRep and UnliftedRep, so that the created Ids have the right
    strictness.
    
    * The RepType.RepType type was removed, as it didn't seem to help with
    * much.
    
    * The RepType.repType function is also removed, in favor of typePrimRep.
    
    * I have waffled a good deal on whether or not to keep VoidRep in
    TyCon.PrimRep. In the end, I decided to keep it there. PrimRep is *not*
    represented in RuntimeRep, and typePrimRep will never return a list
    including
    VoidRep. But it's handy to have in, e.g., ByteCodeGen and friends. I can
    imagine another design choice where we have a PrimRepV type that is
    PrimRep
    with an extra constructor. That seemed to be a heavier design, though,
    and I'm
    not sure what the benefit would be.
    
    * The last, unused vestiges of # (unliftedTypeKind) have been removed.
    
    * There were several pretty-printing bugs that this change exposed;
    * these are fixed.
    
    * We previously checked for levity polymorphism in the types of binders.
    * But we
    also must exclude levity polymorphism in function arguments. This is
    hard to check
    for, requiring a good deal of care in the desugarer. See Note [Levity
    polymorphism
    checking] in DsMonad.
    
    * In order to efficiently check for levity polymorphism in functions, it
    * was necessary
    to add a new bit of IdInfo. See Note [Levity info] in IdInfo.
    
    * It is now safe for unlifted types to be unsaturated in Core. Core Lint
    * is updated
    accordingly.
    
    * We can only know strictness after zonking, so several checks around
    * strictness
    in the type-checker (checkStrictBinds, the check for unlifted variables
    under a ~
    pattern) have been moved to the desugarer.
    
    * Along the way, I improved the treatment of unlifted vs. banged
    * bindings. See
    Note [Strict binds checks] in DsBinds and #13075.
    
    * Now that we print type-checked source, we must be careful to print
    * ConLikes correctly.
    This is facilitated by a new HsConLikeOut constructor to HsExpr.
    Particularly troublesome
    are unlifted pattern synonyms that get an extra void# argument.
    
    * Includes a submodule update for haddock, getting rid of #.
    
    * New testcases:
      typecheck/should_fail/StrictBinds
      typecheck/should_fail/T12973
      typecheck/should_run/StrictPats
      typecheck/should_run/T12809
      typecheck/should_fail/T13105
      patsyn/should_fail/UnliftedPSBind
      typecheck/should_fail/LevPolyBounded
      typecheck/should_compile/T12987
      typecheck/should_compile/T11736
    
    * Fixed tickets:
      #12809
      #12973
      #11736
      #13075
      #12987
    
    * This also adds a test case for #13105. This test case is
    * "compile_fail" and
    succeeds, because I want the testsuite to monitor the error message.
    When #13105 is fixed, the test case will compile cleanly.
    e7985ed2
TcBinds.hs 66.1 KB