Refactor tuple constraints

Make tuple constraints be handled by a perfectly ordinary
type class, with the component constraints being the
superclasses:
    class (c1, c2) => (c2, c2)

This change was provoked by

  #10359  inability to re-use a given tuple
          constraint as a whole

  #9858   confusion between term tuples
          and constraint tuples

but it's generally a very nice simplification. We get rid of
 -  In Type, the TuplePred constructor of PredTree,
    and all the code that dealt with TuplePreds
 -  In TcEvidence, the constructors EvTupleMk, EvTupleSel

See Note [How tuples work] in TysWiredIn.

Of course, nothing is ever entirely simple. This one
proved quite fiddly.

- I did quite a bit of renaming, which makes this patch
  touch a lot of modules. In partiuclar tupleCon -> tupleDataCon.

- I made constraint tuples known-key rather than wired-in.
  This is different to boxed/unboxed tuples, but it proved
  awkward to have all the superclass selectors wired-in.
  Easier just to use the standard mechanims.

- While I was fiddling with known-key names, I split the TH Name
  definitions out of DsMeta into a new module THNames.  That meant
  that the known-key names can all be gathered in PrelInfo, without
  causing module loops.

- I found that the parser was parsing an import item like
      T( .. )
  as a *data constructor* T, and then using setRdrNameSpace to
  fix it.  Stupid!  So I changed the parser to parse a *type
  constructor* T, which means less use of setRdrNameSpace.

  I also improved setRdrNameSpace to behave better on Exact Names.
  Largely on priciple; I don't think it matters a lot.

- When compiling a data type declaration for a wired-in thing like
  tuples (,), or lists, we don't really need to look at the
  declaration.  We have the wired-in thing!  And not doing so avoids
  having to line up the uniques for data constructor workers etc.
  See Note [Declarations for wired-in things]

- I found that FunDeps.oclose wasn't taking superclasses into
  account; easily fixed.

- Some error message refactoring for invalid constraints in TcValidity

1 files changed, 5 insertions, 5 deletions

diff --git a/compiler/simplStg/UnariseStg.hs b/compiler/simplStg/UnariseStg.hs
index 0fc6ccf226..f3d592f49c 100644
--- a/compiler/simplStg/UnariseStg.hs
+++ b/compiler/simplStg/UnariseStg.hs
@@ -59,7 +59,7 @@ import BasicTypes
 type UnariseEnv = VarEnv [Id]
 
 ubxTupleId0 :: Id
-ubxTupleId0 = dataConWorkId (tupleCon UnboxedTuple 0)
+ubxTupleId0 = dataConWorkId (tupleDataCon Unboxed 0)
 
 unarise :: UniqSupply -> [StgBinding] -> [StgBinding]
 unarise us binds = zipWith (\us -> unariseBinding us init_env) (listSplitUniqSupply us) binds
@@ -88,7 +88,7 @@ unariseExpr _ rho (StgApp f args)
   , UbxTupleRep tys <- repType (idType f)
   =  -- Particularly important where (##) is concerned
      -- See Note [Nullary unboxed tuple]
-    StgConApp (tupleCon UnboxedTuple (length tys))
+    StgConApp (tupleDataCon Unboxed (length tys))
               (map StgVarArg (unariseId rho f))
 
   | otherwise
@@ -98,7 +98,7 @@ unariseExpr _ _ (StgLit l)
   = StgLit l
 
 unariseExpr _ rho (StgConApp dc args)
-  | isUnboxedTupleCon dc = StgConApp (tupleCon UnboxedTuple (length args')) args'
+  | isUnboxedTupleCon dc = StgConApp (tupleDataCon Unboxed (length args')) args'
   | otherwise            = StgConApp dc args'
   where
     args' = unariseArgs rho args
@@ -139,14 +139,14 @@ unariseAlts us rho alt_ty _ (UnaryRep _) alts
   = (alt_ty, zipWith (\us alt -> unariseAlt us rho alt) (listSplitUniqSupply us) alts)
 
 unariseAlts us rho _ bndr (UbxTupleRep tys) ((DEFAULT, [], [], e) : _)
-  = (UbxTupAlt n, [(DataAlt (tupleCon UnboxedTuple n), ys, uses, unariseExpr us2' rho' e)])
+  = (UbxTupAlt n, [(DataAlt (tupleDataCon Unboxed n), ys, uses, unariseExpr us2' rho' e)])
   where
     (us2', rho', ys) = unariseIdBinder us rho bndr
     uses = replicate (length ys) (not (isDeadBinder bndr))
     n = length tys
 
 unariseAlts us rho _ bndr (UbxTupleRep _) [(DataAlt _, ys, uses, e)]
-  = (UbxTupAlt n, [(DataAlt (tupleCon UnboxedTuple n), ys', uses', unariseExpr us2' rho'' e)])
+  = (UbxTupAlt n, [(DataAlt (tupleDataCon Unboxed n), ys', uses', unariseExpr us2' rho'' e)])
   where
     (us2', rho', ys', uses') = unariseUsedIdBinders us rho ys uses
     rho'' = extendVarEnv rho' bndr ys'