diff options
Diffstat (limited to 'compiler/GHC/Utils/Misc.hs')
| -rw-r--r-- | compiler/GHC/Utils/Misc.hs | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/compiler/GHC/Utils/Misc.hs b/compiler/GHC/Utils/Misc.hs index f7168190e4..abd85b6b66 100644 --- a/compiler/GHC/Utils/Misc.hs +++ b/compiler/GHC/Utils/Misc.hs @@ -43,7 +43,7 @@ module GHC.Utils.Misc ( listLengthCmp, atLength, equalLength, compareLength, leLength, ltLength, - isSingleton, only, GHC.Utils.Misc.singleton, + isSingleton, only, expectOnly, GHC.Utils.Misc.singleton, notNull, snocView, isIn, isn'tIn, @@ -563,6 +563,18 @@ only (a:_) = a #endif only _ = panic "Util: only" +-- | Extract the single element of a list and panic with the given message if +-- there are more elements or the list was empty. +-- Like 'expectJust', but for lists. +expectOnly :: HasCallStack => String -> [a] -> a +{-# INLINE expectOnly #-} +#if defined(DEBUG) +expectOnly _ [a] = a +#else +expectOnly _ (a:_) = a +#endif +expectOnly msg _ = panic ("expectOnly: " ++ msg) + -- Debugging/specialising versions of \tr{elem} and \tr{notElem} # if !defined(DEBUG) |