Fix Trac #959: a long-standing bug in instantiating otherwise-unbound type variables

[ghc-hetmet.git] / compiler / types / TyCon.lhs

diff --git a/compiler/types/TyCon.lhs b/compiler/types/TyCon.lhs
index bb21536..6f8803c 100644 (file)
--- a/compiler/types/TyCon.lhs
+++ b/compiler/types/TyCon.lhs
@@ -20,13 +20,14 @@ module TyCon(
        mkClassTyCon,
        mkFunTyCon,
        mkPrimTyCon,
-       mkVoidPrimTyCon,
+       mkKindTyCon,
        mkLiftedPrimTyCon,
        mkTupleTyCon,
        mkSynTyCon,
         mkSuperKindTyCon,
         mkCoercionTyCon,
         mkForeignTyCon,
+        mkAnyTyCon,
 
         -- ** Predicates on TyCons
         isAlgTyCon,
@@ -37,7 +38,7 @@ module TyCon(
         isSynTyCon, isClosedSynTyCon, isOpenSynTyCon,
         isSuperKindTyCon,
         isCoercionTyCon, isCoercionTyCon_maybe,
-        isForeignTyCon,
+        isForeignTyCon, isAnyTyCon,
 
        isInjectiveTyCon,
        isDataTyCon, isProductTyCon, isEnumerationTyCon, 
@@ -103,7 +104,7 @@ import Data.List( elemIndex )
 %************************************************************************
 
 \begin{code}
--- | Represents type constructors. Type constructors are introduced by things such as:
+-- | TyCons represent type constructors. Type constructors are introduced by things such as:
 --
 -- 1) Data declarations: @data Foo = ...@ creates the @Foo@ type constructor of kind @*@
 --
@@ -150,6 +151,7 @@ data TyCon
                                        -- that doesn't mean it's a true GADT; only that the "where"
                                        --      form was used. This field is used only to guide
                                        --      pretty-printing
+
        algTcStupidTheta :: [PredType], -- ^ The \"stupid theta\" for the data type (always empty for GADTs).
                                        -- A \"stupid theta\" is the context to the left of an algebraic type
                                        -- declaration, e.g. @Eq a@ in the declaration @data Eq a => T a ...@.
@@ -198,17 +200,19 @@ data TyCon
        tyConUnique   :: Unique,
        tyConName     :: Name,
        tyConKind     :: Kind,
-       tyConArity    :: Arity,         -- SLPJ Oct06: I'm not sure what the significance
-                                       --             of the arity of a primtycon is!
+       tyConArity    :: Arity,                 -- SLPJ Oct06: I'm not sure what the significance
+                                               --             of the arity of a primtycon is!
+
+       primTyConRep  :: PrimRep,               -- ^ Many primitive tycons are unboxed, but some are
+                                                       --   boxed (represented by pointers). This 'PrimRep' holds
+                                               --   that information.
+                                               -- Only relevant if tyConKind = *
 
-       primTyConRep  :: PrimRep,
-                       -- ^ Many primitive tycons are unboxed, but some are
-                       -- boxed (represented by pointers). This 'PrimRep' holds
-                       -- that information
+       isUnLifted   :: Bool,                   -- ^ Most primitive tycons are unlifted (may not contain bottom)
+                                               --   but foreign-imported ones may be lifted
 
-       isUnLifted   :: Bool,           -- ^ Most primitive tycons are unlifted (may not contain bottom)
-                                       -- but foreign-imported ones may be lifted
-       tyConExtName :: Maybe FastString        -- ^ @Just e@ for foreign-imported types, holds the name of the imported thing
+       tyConExtName :: Maybe FastString        -- ^ @Just e@ for foreign-imported types, 
+                                                --   holds the name of the imported thing
     }
 
   -- | Type coercions, such as @(~)@, @sym@, @trans@, @left@ and @right@.
@@ -226,6 +230,19 @@ data TyCon
                --      the kind as a pair of types: @(ta, tc)@
     }
 
+  -- | Any types.  Like tuples, this is a potentially-infinite family of TyCons
+  --   one for each distinct Kind. They have no values at all.
+  --   Because there are infinitely many of them (like tuples) they are 
+  --   defined in GHC.Prim and have names like "Any(*->*)".  
+  --   Their Unique is derived from the OccName.
+  -- See Note [Any types] in TysPrim
+  | AnyTyCon {
+       tyConUnique  :: Unique,
+       tyConName    :: Name,
+       tyConKind    :: Kind    -- Never = *; that is done via PrimTyCon
+                               -- See Note [Any types] in TysPrim
+    }
+
   -- | Super-kinds. These are "kinds-of-kinds" and are never seen in Haskell source programs.
   -- There are only two super-kinds: TY (aka "box"), which is the super-kind of kinds that 
   -- construct types eventually, and CO (aka "diamond"), which is the super-kind of kinds
@@ -643,10 +660,10 @@ mkPrimTyCon :: Name  -> Kind -> Arity -> PrimRep -> TyCon
 mkPrimTyCon name kind arity rep
   = mkPrimTyCon' name kind arity rep True  
 
--- | Create the special void 'TyCon' which is unlifted and has 'VoidRep'
-mkVoidPrimTyCon :: Name -> Kind -> Arity -> TyCon
-mkVoidPrimTyCon name kind arity 
-  = mkPrimTyCon' name kind arity VoidRep True  
+-- | Kind constructors
+mkKindTyCon :: Name -> Kind -> TyCon
+mkKindTyCon name kind
+  = mkPrimTyCon' name kind 0 VoidRep True  
 
 -- | Create a lifted primitive 'TyCon' such as @RealWorld@
 mkLiftedPrimTyCon :: Name  -> Kind -> Arity -> PrimRep -> TyCon
@@ -688,6 +705,12 @@ mkCoercionTyCon name arity kindRule
         coKindFun = kindRule
     }
 
+mkAnyTyCon :: Name -> Kind -> TyCon
+mkAnyTyCon name kind 
+  = AnyTyCon { tyConName = name,
+               tyConKind = kind,
+               tyConUnique = nameUnique name }
+
 -- | Create a super-kind 'TyCon'
 mkSuperKindTyCon :: Name -> TyCon -- Super kinds always have arity zero
 mkSuperKindTyCon name
@@ -907,6 +930,11 @@ isSuperKindTyCon :: TyCon -> Bool
 isSuperKindTyCon (SuperKindTyCon {}) = True
 isSuperKindTyCon _                   = False
 
+-- | Is this an AnyTyCon?
+isAnyTyCon :: TyCon -> Bool
+isAnyTyCon (AnyTyCon {}) = True
+isAnyTyCon _              = False
+
 -- | Attempt to pull a 'TyCon' apart into the arity and 'coKindFun' of
 -- a coercion 'TyCon'. Returns @Nothing@ if the 'TyCon' is not of the
 -- appropriate kind