Tidy-up sweep, following the Great Skolemisation Simplification

[ghc-hetmet.git] / compiler / typecheck / TcPat.lhs

diff --git a/compiler/typecheck/TcPat.lhs b/compiler/typecheck/TcPat.lhs
index f8c98b5..7cb16de 100644 (file)
--- a/compiler/typecheck/TcPat.lhs
+++ b/compiler/typecheck/TcPat.lhs
@@ -32,7 +32,6 @@ import Coercion
 import StaticFlags
 import TyCon
 import DataCon
-import VarSet  ( emptyVarSet )
 import PrelNames
 import BasicTypes hiding (SuccessFlag(..))
 import DynFlags
@@ -59,14 +58,13 @@ tcLetPat :: TcSigFun -> LetBndrSpec
 tcLetPat sig_fn no_gen pat pat_ty thing_inside
   = tc_lpat pat pat_ty penv thing_inside 
   where
-    penv = PE { pe_res_tvs = emptyVarSet, pe_lazy = True
+    penv = PE { pe_lazy = True
               , pe_ctxt = LetPat sig_fn no_gen }
 
 -----------------
 tcPats :: HsMatchContext Name
        -> [LPat Name]           -- Patterns,
        -> [TcSigmaType]                 --   and their types
-       -> TcRhoType             -- Result type,
        -> TcM a                  --   and the checker for the body
        -> TcM ([LPat TcId], a)
 
@@ -81,39 +79,27 @@ tcPats :: HsMatchContext Name
 --   3. Check the body
 --   4. Check that no existentials escape
 
-tcPats ctxt pats pat_tys res_ty thing_inside
+tcPats ctxt pats pat_tys thing_inside
   = tc_lpats penv pats pat_tys thing_inside
   where
-    penv = PE { pe_res_tvs = tyVarsOfTypes (res_ty : pat_tys)
-              , pe_lazy = False
-              , pe_ctxt = LamPat ctxt }
+    penv = PE { pe_lazy = False, pe_ctxt = LamPat ctxt }
 
 tcPat :: HsMatchContext Name
       -> LPat Name -> TcSigmaType 
-      -> TcRhoType             -- Result type
       -> TcM a                 -- Checker for body, given
                                -- its result type
       -> TcM (LPat TcId, a)
-tcPat ctxt pat pat_ty res_ty thing_inside
+tcPat ctxt pat pat_ty thing_inside
   = tc_lpat pat pat_ty penv thing_inside
   where
-    penv = PE { pe_res_tvs = tyVarsOfTypes [res_ty, pat_ty]
-              , pe_lazy = False
-              , pe_ctxt = LamPat ctxt }
+    penv = PE { pe_lazy = False, pe_ctxt = LamPat ctxt }
    
 
 -----------------
 data PatEnv
-  = PE { pe_res_tvs :: TcTyVarSet      
-                  -- For existential escape check; see Note [Existential check]
-                  -- Nothing <=> inside a "~"
-                  -- Just tvs <=> unification tvs free in the result
-                  --              (which should be made untouchable in
-                  --               any existentials we encounter in the pattern)
-
-       , pe_lazy :: Bool       -- True <=> lazy context, so no existentials allowed
+  = PE { pe_lazy :: Bool       -- True <=> lazy context, so no existentials allowed
        , pe_ctxt :: PatCtxt    -- Context in which the whole pattern appears
-    }
+       }
 
 data PatCtxt
   = LamPat   -- Used for lambdas, case etc
@@ -188,7 +174,7 @@ Note [Existential check]
 Lazy patterns can't bind existentials.  They arise in two ways:
   * Let bindings      let { C a b = e } in b
   * Twiddle patterns  f ~(C a b) = e
-The pe_res_tvs field of PatEnv says whether we are inside a lazy
+The pe_lazy field of PatEnv says whether we are inside a lazy
 pattern (perhaps deeply)
 
 If we aren't inside a lazy pattern then we can bind existentials,
@@ -736,17 +722,8 @@ tcConPat penv (L con_span con_name) pat_ty arg_pats thing_inside
                  -- should require the GADT language flag
 
        ; given <- newEvVars theta'
-        ; let free_tvs = pe_res_tvs penv
-               -- Since we have done checkExistentials,
-               -- pe_res_tvs can only be Just at this point
-               --
-               -- Nor do we need pat_ty, because we've put all the
-               -- unification variables in right at the start when
-               -- initialising the PatEnv; and the pattern itself
-               -- only adds skolems.
-
         ; (ev_binds, (arg_pats', res))
-            <- checkConstraints skol_info free_tvs ex_tvs' given $
+            <- checkConstraints skol_info ex_tvs' given $
                 tcConArgs data_con arg_tys' arg_pats penv thing_inside
 
         ; let res_pat = ConPatOut { pat_con   = L con_span data_con,