Hurrah! This major commit adds support for scoped kind variables,

which (finally) fills out the functionality of polymorphic kinds.
It also fixes numerous bugs.

Main changes are:

Renaming stuff
~~~~~~~~~~~~~~
* New type in HsTypes:
     data HsBndrSig sig = HsBSig sig [Name]
  which is used for type signatures in patterns, and kind signatures
  in types.  So when you say
       f (x :: [a]) = x ++ x
  or
       data T (f :: k -> *) (x :: *) = MkT (f x)
  the signatures in both cases are a HsBndrSig.

* The [Name] in HsBndrSig records the variables bound by the
  pattern, that is 'a' in the first example, 'k' in the second,
  and nothing in the third.  The renamer initialises the field.

* As a result I was able to get rid of
     RnHsSyn.extractHsTyNames :: LHsType Name -> NameSet
  and its friends altogether.  Deleted the entire module!
  This led to some knock-on refactoring; in particular the
  type renamer now returns the free variables just like the
  term renamer.

Kind-checking types: mainly TcHsType
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A major change is that instead of kind-checking types in two
passes, we now do one. Under the old scheme, the first pass did
kind-checking and (hackily) annotated the HsType with the
inferred kinds; and the second pass desugared the HsType to a
Type.  But now that we have kind variables inside types, the
first pass (TcHsType.tc_hs_type) can go straight to Type, and
zonking will squeeze out any kind unification variables later.

This is much nicer, but it was much more fiddly than I had expected.

The nastiest corner is this: it's very important that tc_hs_type
uses lazy constructors to build the returned type. See
Note [Zonking inside the knot] in TcHsType.

Type-checking type and class declarations: mainly TcTyClsDecls
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I did tons of refactoring in TcTyClsDecls.  Simpler and nicer now.

Typechecking bindings: mainly TcBinds
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I rejigged (yet again) the handling of type signatures in TcBinds.
It's a bit simpler now.  The main change is that tcTySigs goes
right through to a TcSigInfo in one step; previously it was split
into two, part here and part later.

Unsafe coercions
~~~~~~~~~~~~~~~~
Usually equality coercions have exactly the same kind on both
sides.  But we do allow an *unsafe* coercion between Int# and Bool,
say, used in
    case error Bool "flah" of { True -> 3#; False -> 0# }
-->
    (error Bool "flah") |> unsafeCoerce Bool Int#

So what is the instantiation of (~#) here?
   unsafeCoerce Bool Int# :: (~#) ??? Bool Int#
I'm using OpenKind here for now, but it's un-satisfying that
the lhs and rhs of the ~ don't have precisely the same kind.

More minor
~~~~~~~~~~
* HsDecl.TySynonym has its free variables attached, which makes
  the cycle computation in TcTyDecls.mkSynEdges easier.

* Fixed a nasty reversed-comparison bug in FamInstEnv:
  @@ -490,7 +490,7 @@ lookup_fam_inst_env' match_fun one_sided ie fam tys
     n_tys = length tys
     extra_tys = drop arity tys
     (match_tys, add_extra_tys)
-       | arity > n_tys = (take arity tys, \res_tys -> res_tys ++ extra_tys)
+       | arity < n_tys = (take arity tys, \res_tys -> res_tys ++ extra_tys)
        | otherwise     = (tys,            \res_tys -> res_tys)

1 files changed, 4 insertions, 5 deletions

diff --git a/compiler/rename/RnExpr.lhs b/compiler/rename/RnExpr.lhs
index 7caae61027..b884d4abde 100644
--- a/compiler/rename/RnExpr.lhs
+++ b/compiler/rename/RnExpr.lhs
@@ -34,8 +34,7 @@ import HsSyn
 import TcRnMonad
 import TcEnv		( thRnBrack )
 import RnEnv
-import RnTypes		( rnHsTypeFVs, rnSplice, rnIPName, checkTH,
-			  mkOpFormRn, mkOpAppRn, mkNegAppRn, checkSectionPrec)
+import RnTypes	
 import RnPat
 import DynFlags
 import BasicTypes	( FixityDirection(..) )
@@ -270,7 +269,7 @@ rnExpr (RecordUpd expr rbinds _ _ _)
 		  fvExpr `plusFV` fvRbinds) }
 
 rnExpr (ExprWithTySig expr pty)
-  = do	{ (pty', fvTy) <- rnHsTypeFVs ExprWithTySigCtx pty
+  = do	{ (pty', fvTy) <- rnLHsType ExprWithTySigCtx pty
 	; (expr', fvExpr) <- bindSigTyVarsFV (hsExplicitTvs pty') $
 		  	     rnLExpr expr
 	; return (ExprWithTySig expr' pty', fvExpr `plusFV` fvTy) }
@@ -283,7 +282,7 @@ rnExpr (HsIf _ p b1 b2)
        ; return (HsIf mb_ite p' b1' b2', plusFVs [fvITE, fvP, fvB1, fvB2]) }
 
 rnExpr (HsType a)
-  = rnHsTypeFVs HsTypeCtx a	`thenM` \ (t, fvT) -> 
+  = rnLHsType HsTypeCtx a	`thenM` \ (t, fvT) -> 
     return (HsType t, fvT)
 
 rnExpr (ArithSeq _ seq)
@@ -607,7 +606,7 @@ rnBracket (ExpBr e) = do { (e', fvs) <- rnLExpr e
 
 rnBracket (PatBr p) = rnPat ThPatQuote p $ \ p' -> return (PatBr p', emptyFVs)
 
-rnBracket (TypBr t) = do { (t', fvs) <- rnHsTypeFVs TypBrCtx t
+rnBracket (TypBr t) = do { (t', fvs) <- rnLHsType TypBrCtx t
 			 ; return (TypBr t', fvs) }
 
 rnBracket (DecBrL decls)