diff --git a/Data/Syntax/Pretty.hs b/Data/Syntax/Pretty.hs
--- a/Data/Syntax/Pretty.hs
+++ b/Data/Syntax/Pretty.hs
@@ -21,6 +21,7 @@
 import           Data.Monoid
 import           Data.SemiIsoFunctor
 import           Data.Syntax
+import           Data.Syntax.Char
 import           Data.Text (Text)
 import qualified Data.Text as T
 import qualified Text.PrettyPrint as P
@@ -42,16 +43,28 @@
     siempty = Printer (\_ -> Left "error")
     (Printer f) /|/ (Printer g) = Printer (\a -> f a <|> g a)
 
+instance SemiIsoMonad Printer where
+    (Printer f) //= g = Printer (\(a, b) -> (<>) <$> f a <*> runPrinter (g a) b)
+
+instance SemiIsoFix Printer where
+    sifix f = Printer $ \a -> runPrinter (f a) a
+
 printText :: Text -> Either String P.Doc
 printText = Right . P.text . T.unpack
 
 instance Syntax Printer Text where
-   anyChar = Printer (Right . P.char)
-   take n = Printer (printText . T.take n)
-   takeWhile p = Printer (printText . T.takeWhile p)
-   takeWhile1 p = Printer (printText <=< notNull . T.takeWhile p)
-     where notNull t | T.null t  = Left "takeWhile1: failed"
-                     | otherwise = Right t
-   takeTill1 p = Printer (printText <=< notNull . T.takeWhile p)
-     where notNull t | T.null t  = Left "takeTill1: failed"
-                     | otherwise = Right t
+    anyChar = Printer (Right . P.char)
+    take n = Printer (printText . T.take n)
+    takeWhile p = Printer (printText . T.takeWhile p)
+    takeWhile1 p = Printer (printText <=< notNull . T.takeWhile p)
+      where notNull t | T.null t  = Left "takeWhile1: failed"
+                      | otherwise = Right t
+    takeTill1 p = Printer (printText <=< notNull . T.takeWhile p)
+      where notNull t | T.null t  = Left "takeTill1: failed"
+                      | otherwise = Right t
+
+instance SyntaxChar Printer Text where
+    decimal = Printer (format . toInteger)
+      where format i | i < 0 = Left "decimal: negative number"
+                     | otherwise = Right (P.integer i)
+    scientific = Printer (Right . P.text . show)
diff --git a/syntax-pretty.cabal b/syntax-pretty.cabal
--- a/syntax-pretty.cabal
+++ b/syntax-pretty.cabal
@@ -1,5 +1,5 @@
 name:                syntax-pretty
-version:             0.1.0.1
+version:             0.2.0.0
 synopsis:            Syntax instance for pretty, the pretty printing library.
 license:             MIT
 license-file:        LICENSE
@@ -16,5 +16,5 @@
 
 library
   exposed-modules:     Data.Syntax.Pretty
-  build-depends:       base >= 4 && < 5, syntax, pretty, semi-iso, text
+  build-depends:       base >= 4 && < 5, syntax >= 0.2, pretty, semi-iso >= 0.3, text, scientific >= 0.3
   default-language:    Haskell2010