1. 13 Dec, 2004 1 commit
  2. 30 Sep, 2004 1 commit
    • simonpj's avatar
      [project @ 2004-09-30 10:35:15 by simonpj] · 23f40f0e
      simonpj authored
      ------------------------------------
      	Add Generalised Algebraic Data Types
      	------------------------------------
      
      This rather big commit adds support for GADTs.  For example,
      
          data Term a where
       	  Lit :: Int -> Term Int
      	  App :: Term (a->b) -> Term a -> Term b
      	  If  :: Term Bool -> Term a -> Term a
      	  ..etc..
      
          eval :: Term a -> a
          eval (Lit i) = i
          eval (App a b) = eval a (eval b)
          eval (If p q r) | eval p    = eval q
          		    | otherwise = eval r
      
      
      Lots and lots of of related changes throughout the compiler to make
      this fit nicely.
      
      One important change, only loosely related to GADTs, is that skolem
      constants in the typechecker are genuinely immutable and constant, so
      we often get better error messages from the type checker.  See
      TcType.TcTyVarDetails.
      
      There's a new module types/Unify.lhs, which has purely-functional
      unification and matching for Type. This is used both in the typechecker
      (for type refinement of GADTs) and in Core Lint (also for type refinement).
      23f40f0e
  3. 12 Feb, 2004 1 commit
  4. 30 Dec, 2003 1 commit
    • simonpj's avatar
      [project @ 2003-12-30 16:29:17 by simonpj] · f714e6b6
      simonpj authored
      ----------------------------
              Re-do kind inference (again)
      	----------------------------
      
         [WARNING: interface file binary representation has
         (as usual) changed slightly; recompile your libraries!]
      
      Inspired by the lambda-cube, for some time GHC has used
      	type Kind = Type
      That is, kinds were represented by the same data type as types.
      
      But GHC also supports unboxed types and unboxed tuples, and these
      complicate the kind system by requiring a sub-kind relationship.
      Notably, an unboxed tuple is acceptable as the *result* of a
      function but not as an *argument*.  So we have the following setup:
      
      		 ?
      		/ \
      	       /   \
      	      ??   (#)
      	     /  \
                  *   #
      
      where	*    [LiftedTypeKind]   means a lifted type
      	#    [UnliftedTypeKind] means an unlifted type
      	(#)  [UbxTupleKind]     means unboxed tuple
      	??   [ArgTypeKind]      is the lub of *,#
      	?    [OpenTypeKind]	means any type at all
      
      In particular:
      
        error :: forall a:?. String -> a
        (->)  :: ?? -> ? -> *
        (\(x::t) -> ...)	Here t::?? (i.e. not unboxed tuple)
      
      All this has beome rather difficult to accommodate with Kind=Type, so this
      commit splits the two.
      
        * Kind is a distinct type, defined in types/Kind.lhs
      
        * IfaceType.IfaceKind disappears: we just re-use Kind.Kind
      
        * TcUnify.unifyKind is a distinct unifier for kinds
      
        * TyCon no longer needs KindCon and SuperKindCon variants
      
        * TcUnify.zapExpectedType takes an expected Kind now, so that
          in TcPat.tcMonoPatBndr we can express that the bound variable
          must have an argTypeKind (??).
      
      The big change is really that kind inference is much more systematic and
      well behaved.  In particular, a kind variable can unify only with a
      "simple kind", which is built from * and (->).  This deals neatly
      with awkward questions about how we can combine sub-kinding with type
      inference.
      
      Lots of small consequential changes, especially to the kind-checking
      plumbing in TcTyClsDecls.  (We played a bit fast and loose before, and
      now we have to be more honest, in particular about how kind inference
      works for type synonyms.  They can have kinds like (* -> #), so
      
      This cures two long-standing SourceForge bugs
      
      * 753777 (tcfail115.hs), which used erroneously to pass,
        but crashed in the code generator
            type T a = Int -> (# Int, Int #)
            f :: T a -> T a
            f t = \x -> case t x of r -> r
      
      * 753780 (tc167.hs), which used erroneously to fail
            f :: (->) Int# Int#
      
      
      Still, the result is not entirely satisfactory.  In particular
      
      * The error message from tcfail115 is pretty obscure
      
      * SourceForge bug 807249 (Instance match failure on openTypeKind)
        is not fixed.  Alas.
      f714e6b6
  5. 02 Dec, 1998 1 commit
  6. 08 Jan, 1998 1 commit
    • simonm's avatar
      [project @ 1998-01-08 18:03:08 by simonm] · 9dd6e1c2
      simonm authored
      The Great Multi-Parameter Type Classes Merge.
      
      Notes from Simon (abridged):
      
      * Multi-parameter type classes are fully implemented.
      * Error messages from the type checker should be noticeably improved
      * Warnings for unused bindings (-fwarn-unused-names)
      * many other minor bug fixes.
      
      Internally there are the following changes
      
      * Removal of Haskell 1.2 compatibility.
      * Dramatic clean-up of the PprStyle stuff.
      * The type Type has been substantially changed.
      * The dictionary for each class is represented by a new
        data type for that purpose, rather than by a tuple.
      9dd6e1c2
  7. 05 Jun, 1997 1 commit
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  13. 30 Apr, 1996 1 commit
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  16. 19 Mar, 1996 1 commit