diff --git a/Data/LinearProgram/GLPK/IO.hs b/Data/LinearProgram/GLPK/IO.hs
--- a/Data/LinearProgram/GLPK/IO.hs
+++ b/Data/LinearProgram/GLPK/IO.hs
@@ -9,8 +9,8 @@
 {-# SPECIALIZE readLP :: (Ord v, Read v) => FilePath -> IO (LP v Double) #-}
 -- | Read a linear program from a file in CPLEX LP format.  Warning: this will not necessarily succeed
 -- on all files generated by 'writeLP', as variable names may be changed.
-readLP :: (Ord v, Read v, Ord c, Fractional c, Group c) => FilePath -> IO (LP v c)
-readLP = fmap (mapVars read . mapVals realToFrac) . readLP'
+readLP :: (Ord v, Read v, Fractional c) => FilePath -> IO (LP v c)
+readLP = fmap (mapVals realToFrac . mapVars read) . readLP'
 
 -- | Read a linear program from a file in CPLEX LP format.
 readLP' :: FilePath -> IO (LP String Double)
diff --git a/Data/LinearProgram/LPMonad.hs b/Data/LinearProgram/LPMonad.hs
--- a/Data/LinearProgram/LPMonad.hs
+++ b/Data/LinearProgram/LPMonad.hs
@@ -6,6 +6,8 @@
 -- for example separating different families of constraints in the problem specification.
 -- 
 -- Many of these functions should be executed in either the @'LPM' v c@ or the @'LPT' v c 'IO'@ monad.
+-- If you wish to generate new variables on an ad-hoc basis, rather than supplying your own variable type, use the
+-- 'VarSource' or 'VarSourceT' monads in your transformer stack.
 module Data.LinearProgram.LPMonad (
 	module Data.LinearProgram.LPMonad.Internal,
 	module Data.LinearProgram.LPMonad.VarSource,
@@ -76,13 +78,13 @@
 	FilePath -> m ()
 writeLPToFile file = get >>= liftIO . writeLP file 
 
-{-# SPECIALIZE readLPFromFile :: (Ord v, Read v, Ord c, Fractional c, Module r c) => FilePath -> LPT v c IO () #-}
+{-# SPECIALIZE readLPFromFile :: (Ord v, Read v, Fractional c) => FilePath -> LPT v c IO () #-}
 -- | Reads a linear program from the specified file in CPLEX LP format, overwriting
 -- the current linear program.  Uses 'read' and 'realToFrac' to translate to the specified type.
 -- Warning: this may not work on all files written using 'writeLPToFile', since variable names
 -- may be changed.
 -- (This is a binding to GLPK, not a Haskell implementation of CPLEX.)
-readLPFromFile :: (Ord v, Read v, Ord c, Fractional c, Group c, MonadState (LP v c) m, MonadIO m) =>
+readLPFromFile :: (Ord v, Read v, Fractional c, MonadState (LP v c) m, MonadIO m) =>
 	FilePath -> m ()
 readLPFromFile = put <=< liftIO . readLP
 
diff --git a/Data/LinearProgram/LPMonad/VarSource.hs b/Data/LinearProgram/LPMonad/VarSource.hs
--- a/Data/LinearProgram/LPMonad/VarSource.hs
+++ b/Data/LinearProgram/LPMonad/VarSource.hs
@@ -1,7 +1,8 @@
 {-# LANGUAGE UndecidableInstances, FlexibleInstances, GeneralizedNewtypeDeriving, FunctionalDependencies, MultiParamTypeClasses #-}
 module Data.LinearProgram.LPMonad.VarSource (
-	-- * Types for automatically generating distinct variables
-	VarSource, VarSourceT, Var, MonadSource(..), evalVarSource, evalVarSourceT) where
+	-- * Variable generation monad
+	VarSource, evalVarSource, VarSourceT, evalVarSourceT, Var(..),
+	MonadSource(..)) where
 
 import Control.Monad
 import Control.Monad.State.Strict
@@ -36,6 +37,7 @@
 
 instance Read Var where
 	readsPrec _ ('x':'_':xs) = [(Var x, s') | (x, s') <- readsPrec 0 xs]
+	readsPrec _ _ = []
 
 instance MonadState s m => MonadState s (VarSourceT m) where
 	put x = VarSourceT (lift (put x))
diff --git a/Data/LinearProgram/Spec.hs b/Data/LinearProgram/Spec.hs
--- a/Data/LinearProgram/Spec.hs
+++ b/Data/LinearProgram/Spec.hs
@@ -114,6 +114,7 @@
 			char '=' >> return EQ,
 			char '>' >> optional (char '=') >> return GT]
 
+{-# SPECIALIZE mapVars :: Ord v' => (v -> v') -> LP v Double -> LP v' Double #-}
 -- | Applies the specified function to the variables in the linear program.
 -- If multiple variables in the original program are mapped to the same variable in the new program,
 -- in general, we set those variables to all be equal, as follows.
diff --git a/glpk-hs.cabal b/glpk-hs.cabal
--- a/glpk-hs.cabal
+++ b/glpk-hs.cabal
@@ -1,5 +1,5 @@
 Name:           glpk-hs
-Version:        0.2.2
+Version:        0.2.3
 Author:         Louis Wasserman
 License:        GPL
 License-file:   LICENSE