diff --git a/Biobase/Secondary.hs b/Biobase/Secondary.hs
--- a/Biobase/Secondary.hs
+++ b/Biobase/Secondary.hs
@@ -38,28 +38,6 @@
   = (c',x',y')
   | otherwise = error $ "can't convert string: " ++ s
 
--- | A basepair is simply a pair of Ints which are 0-indexing a sequence.
---
--- TODO storable vector, newtype, peek/poke?
-
-type PairIdx = (Int,Int)
-
--- | A pair as a tuple containing 'Nuc's.
-
-type Pair = (Nuc,Nuc)
-
--- | Annotation for a basepair.
-
-type ExtPairAnnotation = (CTisomerism,Edge,Edge)
-
--- | An extended basepair is a basepair, annotated with edge and CTisomerism.
-
-type ExtPairIdx = (PairIdx,ExtPairAnnotation)
-
--- | An extended basepair, with nucleotides an annotation.
-
-type ExtPair = (Pair,ExtPairAnnotation)
-
 -- | Each nucleotide in a pair may be paired using one of three edges:
 -- watson-crik, sugar, or hoogsteen.
 
@@ -172,11 +150,40 @@
   toEnum   = CT
   fromEnum = unCT
 
--- ** special show instances
 
+
+-- * Types
+
+-- | A basepair is simply a pair of Ints which are 0-indexing a sequence.
+--
+-- TODO storable vector, newtype, peek/poke?
+
+type PairIdx = (Int,Int)
+
+-- | A pair as a tuple containing 'Nuc's.
+
+type Pair = (Nuc,Nuc)
+
+-- | Annotation for a basepair.
+
+type ExtPairAnnotation = (CTisomerism,Edge,Edge)
+
+-- | An extended basepair is a basepair, annotated with edge and CTisomerism.
+
+type ExtPairIdx = (PairIdx,ExtPairAnnotation)
+
+-- | An extended basepair, with nucleotides an annotation.
+
+type ExtPair = (Pair,ExtPairAnnotation)
+
+
+
+-- * special show instances
+
 -- | This one requires ghc head
 --
 -- TODO maybe newtype this triple?
 
 --instance Show (CTisomerism,Edge,Edge) where
 --  show (ct,eI,eJ) = concat [show ct, show eI, show eJ]
+
diff --git a/Biobase/Secondary/Vienna.hs b/Biobase/Secondary/Vienna.hs
new file mode 100644
--- /dev/null
+++ b/Biobase/Secondary/Vienna.hs
@@ -0,0 +1,108 @@
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE StandaloneDeriving #-}
+
+-- | Encoding of Watson-Crick and Wobble Pairs in the Vienna RNA package style.
+
+module Biobase.Secondary.Vienna where
+
+import Data.Ix
+import Data.Primitive.Types
+import qualified Data.Vector.Generic as VG
+import qualified Data.Vector.Generic.Mutable as VGM
+import qualified Data.Vector.Unboxed as VU
+import Data.Tuple (swap)
+
+import Biobase.Primary
+import Biobase.Primary.Bounds
+
+
+
+-- | Use machine Ints internally
+
+newtype ViennaPair = ViennaPair Int
+  deriving (Eq,Ord,Ix)
+
+(vpNP:vpCG:vpGC:vpGU:vpUG:vpAU:vpUA:vpNS:_) = map ViennaPair [0..]
+
+class MkViennaPair a where
+  mkViennaPair :: a -> ViennaPair
+  fromViennaPair :: ViennaPair -> a
+
+instance MkViennaPair (Nuc,Nuc) where
+  mkViennaPair (b1,b2)
+    | b1==nC&&b2==nG = vpCG
+    | b1==nG&&b2==nC = vpGC
+    | b1==nG&&b2==nU = vpGU
+    | b1==nU&&b2==nG = vpUG
+    | b1==nA&&b2==nU = vpAU
+    | b1==nU&&b2==nA = vpUA
+    | otherwise = vpNS
+  fromViennaPair p
+    | p==vpCG = (nC,nG)
+    | p==vpGC = (nG,nC)
+    | p==vpGU = (nG,nU)
+    | p==vpUG = (nU,nG)
+    | p==vpAU = (nA,nU)
+    | p==vpUA = (nU,nA)
+    | otherwise = error "non-standard pairs can't be backcasted"
+
+deriving instance VGM.MVector VU.MVector ViennaPair
+deriving instance VG.Vector VU.Vector ViennaPair
+deriving instance VU.Unbox ViennaPair
+deriving instance Prim ViennaPair
+
+instance Enum ViennaPair where
+  toEnum x
+    | x>=0 && x<=7 = ViennaPair x
+    | otherwise    = error $ "can't make to enum" ++ show x
+  fromEnum (ViennaPair x) = x
+  {-# INLINE toEnum #-}
+  {-# INLINE fromEnum #-}
+
+instance Bounded ViennaPair where
+  minBound = vpNP
+  maxBound = vpNS
+
+instance Bounds ViennaPair where
+  minNormal = vpCG
+  maxNormal = vpUA
+  minExtended = vpNP
+  maxExtended = vpNS
+
+instance Show ViennaPair where
+  show x
+    | Just s <- x `lookup` pairToString = s
+
+instance Read ViennaPair where
+  readsPrec p [] = []
+  readsPrec p [x] = []
+  readsPrec p (x:y:xs)
+    | x ==' ' = readsPrec p (y:xs)
+    | Just n <- (x:y:[]) `lookup` s2p = [(n,xs)]
+    | otherwise = []
+    where s2p = (map swap pairToString)
+
+
+
+-- | reverse a vienna pair
+
+revPair :: ViennaPair -> ViennaPair
+revPair p
+  | p==vpCG = vpGC
+  | p==vpGC = vpCG
+  | p==vpGU = vpUG
+  | p==vpUG = vpGU
+  | p==vpAU = vpUA
+  | p==vpUA = vpAU
+  | p==vpNP = vpNP
+  | p==vpNS = vpNS
+
+
+
+-- * Convenience structures
+
+cguaP = [vpCG..vpUA]
+cgnsP = [vpCG..vpNS]
+pairToString = [(vpCG,"CG"),(vpGC,"GC"),(vpUA,"UA"),(vpAU,"AU"),(vpGU,"GU"),(vpUG,"UG"),(vpNS,"NS"),(vpNP,"NP")]
diff --git a/BiobaseXNA.cabal b/BiobaseXNA.cabal
--- a/BiobaseXNA.cabal
+++ b/BiobaseXNA.cabal
@@ -1,5 +1,5 @@
 name:           BiobaseXNA
-version:        0.5.0.1
+version:        0.5.1.0
 author:         Christian Hoener zu Siederdissen
 maintainer:     choener@tbi.univie.ac.at
 homepage:       http://www.tbi.univie.ac.at/~choener/
@@ -38,6 +38,7 @@
     Biobase.Secondary.Constraint
     Biobase.Secondary.Diagrams
     Biobase.Secondary.PseudoKnots
+    Biobase.Secondary.Vienna
 
   ghc-options:
     -O2