1 files changed, 16 insertions, 2 deletions
diff --git a/libraries/ghc-prim/GHC/Prim/Panic.hs b/libraries/ghc-prim/GHC/Prim/Panic.hs
index a6f1eb588b..a24f82ee07 100644
--- a/libraries/ghc-prim/GHC/Prim/Panic.hs
+++ b/libraries/ghc-prim/GHC/Prim/Panic.hs
@@ -4,6 +4,7 @@
 {-# LANGUAGE UnboxedTuples #-}
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE EmptyCase #-}
+{-# LANGUAGE RankNTypes, KindSignatures #-}
 
 -- | Primitive panics.
 --
@@ -11,12 +12,13 @@
 module GHC.Prim.Panic
    ( absentSumFieldError
    , panicError
-   , absentError
+   , absentError, absentConstraintError
    )
 where
 
 import GHC.Prim
 import GHC.Magic
+import GHC.Types( Type )
 
 default () -- Double and Integer aren't available yet
 
@@ -95,7 +97,7 @@ absentSumFieldError = panicError "entered absent sum field!"#
 
 -- | Displays "Oops!  Entered absent arg" ++ errormsg and exits the program.
 {-# NOINLINE absentError #-}
-absentError :: Addr# -> a
+absentError :: forall (a :: Type). Addr# -> a
 absentError errmsg =
   runRW# (\s ->
     case stg_absentError# errmsg s of
@@ -103,3 +105,15 @@ absentError errmsg =
                     -- use an empty case lest the pattern match
                     -- checker squawks.
                     let x = x in x)
+
+{-# NOINLINE absentConstraintError #-}
+absentConstraintError :: forall (a :: Type). Addr# -> a
+-- We want to give this the type
+--    forall (a :: Constraint). Addr# -> a
+-- but Haskell source code doesn't allow functions that return Constraint
+-- Fortunately, absentConstraintError is a wired-in Id with the above
+-- desired type. So the only purpose of this definition is to give a
+-- function to call. And for that purpose, absentError will do fine.
+-- It's fine to lie about about the type; it is not looked at
+-- because absentConstraintError is wired-in.
+absentConstraintError errmsg = absentError errmsg