Make record selectors into ordinary functions

[ghc-hetmet.git] / compiler / basicTypes / DataCon.lhs

diff --git a/compiler/basicTypes/DataCon.lhs b/compiler/basicTypes/DataCon.lhs
index df8af8e..d8fdfb5 100644 (file)
--- a/compiler/basicTypes/DataCon.lhs
+++ b/compiler/basicTypes/DataCon.lhs
@@ -318,7 +318,6 @@ data DataCon
        dcOrigArgTys :: [Type],         -- Original argument types
                                        -- (before unboxing and flattening of strict fields)
        dcOrigResTy :: Type,            -- Original result type, as seen by the user
-               -- INVARIANT: mentions only dcUnivTyVars
                -- NB: for a data instance, the original user result type may 
                -- differ from the DataCon's representation TyCon.  Example
                --      data instance T [a] where MkT :: a -> T [a]
@@ -636,8 +635,10 @@ dataConFieldLabels = dcFields
 
 -- | Extract the type for any given labelled field of the 'DataCon'
 dataConFieldType :: DataCon -> FieldLabel -> Type
-dataConFieldType con label = expectJust "unexpected label" $
-    lookup label (dcFields con `zip` dcOrigArgTys con)
+dataConFieldType con label
+  = case lookup label (dcFields con `zip` dcOrigArgTys con) of
+      Just ty -> ty
+      Nothing -> pprPanic "dataConFieldType" (ppr con <+> ppr label)
 
 -- | The strictness markings decided on by the compiler.  Does not include those for
 -- existential dictionaries.  The list is in one-to-one correspondence with the arity of the 'DataCon'
@@ -726,7 +727,7 @@ dataConUserType :: DataCon -> Type
 --
 -- rather than:
 --
--- > T :: forall a c. forall b. (c=[a]) => a -> b -> T c
+-- > T :: forall a c. forall b. (c~[a]) => a -> b -> T c
 --
 -- NB: If the constructor is part of a data instance, the result type
 -- mentions the family tycon, not the internal one.