[project @ 1999-04-27 12:34:49 by simonm]

[ghc-hetmet.git] / ghc / compiler / utils / Util.lhs

diff --git a/ghc/compiler/utils/Util.lhs b/ghc/compiler/utils/Util.lhs
index 149ca9d..d9fbaa9 100644 (file)
--- a/ghc/compiler/utils/Util.lhs
+++ b/ghc/compiler/utils/Util.lhs
@@ -15,7 +15,7 @@ module Util (
        zipEqual, zipWithEqual, zipWith3Equal, zipWith4Equal,
         zipLazy, stretchZipEqual,
        mapAndUnzip, mapAndUnzip3,
-       nOfThem, lengthExceeds, isSingleton,
+       nOfThem, lengthExceeds, isSingleton, only,
        snocView,
        isIn, isn'tIn,
 
@@ -188,6 +188,13 @@ isSingleton :: [a] -> Bool
 
 isSingleton [x] = True
 isSingleton  _  = False
+
+only :: [a] -> a
+#ifdef DEBUG
+only [a] = a
+#else
+only (a:_) = a
+#endif
 \end{code}
 
 \begin{code}