PredType for type constraints in the pattern match checker instead of EvVar

Using EvVars for capturing type constraints implied side-effects in DsM
when we just wanted to *construct* type constraints.

But giving names to type constraints is only necessary when passing
Givens to the type checker, of which the majority of the pattern match
checker should be unaware.

Thus, we simply generate `newtype TyCt = TyCt PredType`, which are
nicely stateless. But at the same time this means we have to allocate
EvVars when we want to query the type oracle! So we keep the type oracle
state as `newtype TyState = TySt (Bag EvVar)`, which nicely makes a
distinction between new, unchecked `TyCt`s and the inert set in
`TyState`.

1 files changed, 3 insertions, 3 deletions

diff --git a/compiler/types/TyCoRep.hs b/compiler/types/TyCoRep.hs
index 51ad630372..065efcd417 100644
--- a/compiler/types/TyCoRep.hs
+++ b/compiler/types/TyCoRep.hs
@@ -860,12 +860,12 @@ see Note [Required quantifiers in the type of a term] in TcExpr.
 ********************************************************************** -}
 
 
--- | A type of the form @p@ of kind @Constraint@ represents a value whose type is
+-- | A type of the form @p@ of constraint kind represents a value whose type is
 -- the Haskell predicate @p@, where a predicate is what occurs before
 -- the @=>@ in a Haskell type.
 --
--- We use 'PredType' as documentation to mark those types that we guarantee to have
--- this kind.
+-- We use 'PredType' as documentation to mark those types that we guarantee to
+-- have this kind.
 --
 -- It can be expanded into its representation, but:
 --