Require SemiIsoMonad.

Data/Syntax.hs

@@ -74,6 +74,7 @@ packed = iso otoList fromList
 --
 -- Methods of this class try to mimic "Data.Attoparsec.Text" interface.
 class ( SemiIsoAlternative syn
+      , SemiIsoMonad syn
       , IsSequence seq
       , Eq seq
       , Eq (Element seq)) 

Data/Syntax/Char.hs

@@ -11,10 +11,10 @@ Stability   :  experimental
 
 Common combinators that work with sequences of chars.
 
-There are A LOT of combinators missing.
 -}
 module Data.Syntax.Char (
     SyntaxChar(..),
+    signed,
     spaces,
     spaces_,
     spaces1,
@@ -44,6 +44,12 @@ class (Syntax syn seq, Element seq ~ Char) => SyntaxChar syn seq where
 
     {-# MINIMAL decimal, scientific #-}
 
+-- | A number with an optional leading '+' or '-' sign character.
+signed :: (Num a, SyntaxChar syn seq) => syn a -> syn a
+signed n =  _Negative /$/ S.char '-' */ n
+        /|/ S.char '+' */ n
+        /|/ n
+
 -- | Accepts zero or more spaces. Generates a single space.
 spaces :: SyntaxChar syn seq => syn ()
 spaces = constant (opoint ' ') /$/ S.takeWhile isSpace