diff --git a/Data/RefSerialize.hs b/Data/RefSerialize.hs
--- a/Data/RefSerialize.hs
+++ b/Data/RefSerialize.hs
@@ -230,14 +230,14 @@
 readHexp = ST(\(Stat(c,s,v)) ->
    let us= unpack s
        l=  readHex  us
-   in if Prelude.null l then Left . Error $  "not readable: " ++ us
+   in if Prelude.null l then Left . Error $  "readHexp: not readable: " ++ us
          else let ((x,str2):_)= l
               in Right(Stat(c, pack $ Prelude.dropWhile isSpace str2,v),x) )
    <?> "readHexp "
 
 
 
-showHexp :: (Num a,Integral a) => a -> ST ()
+showHexp :: (Num a,Integral a,Show a) => a -> ST ()
 showHexp var= ST(\(Stat(c,s,v)) ->  Right(Stat(c, s `append` " " `append` (pack $ showHex var ""),v),()))  <?> "showHexp "
 
 -- |if a is an instance of Show, showpText can be used as the showp method
@@ -363,10 +363,10 @@
 readVar :: Serialize c => ST c -> ST c
 readVar (ST f)=  ST(\(Stat(c,s,v))->
      let
-               s1= B.dropWhile isSpace s
-               (var, str2) = B.span isAlphaNum s1
-               str3= B.dropWhile isSpace str2
-               nvar= numVar $ unpack var
+       s1= B.dropWhile isSpace s
+       (var, str2) = B.span isAlphaNum s1
+       str3= B.dropWhile isSpace str2
+       nvar= numVar $ unpack var
 
      in  if B.null var then Left (Error "expected variable name" )
          else
diff --git a/RefSerialize.cabal b/RefSerialize.cabal
--- a/RefSerialize.cabal
+++ b/RefSerialize.cabal
@@ -1,5 +1,5 @@
 name:                RefSerialize
-version:             0.2.8
+version:             0.2.8.1
 synopsis:            Write to and read from Strings maintaining internal memory references
 description:
                      Read, Show and Data.Binary do not check for internal data references to the same address.
@@ -26,6 +26,8 @@
                      See demo.hs and tutorial.
                      .
                      in this release:
+                            .
+                            * 0.2.8.1 fixed problem with showHex  Show constraint in the latter version of Numeric
                             .
                             * Serialization instance now includes an internal wiriter
                             .