diff --git a/Data/LinearProgram/GLPK.hs b/Data/LinearProgram/GLPK.hs
--- a/Data/LinearProgram/GLPK.hs
+++ b/Data/LinearProgram/GLPK.hs
@@ -1,10 +1,11 @@
 {-# OPTIONS -funbox-strict-fields #-}
-{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE TupleSections, RecordWildCards #-}
 
 module Data.LinearProgram.GLPK (GLPOpts(..), MsgLev(..), BranchingTechnique(..),
-	BacktrackTechnique(..), Preprocessing(..), Cuts(..), 
+	BacktrackTechnique(..), Preprocessing(..), Cuts(..), ReturnCode(..), 
 	simplexDefaults, mipDefaults, glpSolveVars, glpSolveAll) where
 
+import Control.Monad
 import Control.Monad.Trans
 
 -- import Debug.Trace
@@ -36,58 +37,62 @@
 
 -- | Solves the linear or mixed integer programming problem.  Returns
 -- the value of the objective function, and the values of the variables.
-glpSolveVars :: (Ord v, Show v, Real c) => GLPOpts -> LP v c -> IO (Double, Map v Double)
+glpSolveVars :: (Ord v, Show v, Real c) => GLPOpts -> LP v c -> IO (ReturnCode, Maybe (Double, Map v Double))
 glpSolveVars opts@SimplexOpts{} lp = runGLPK $ do
-	Just vars <- doGLP opts lp
-	obj <- getObjVal
-	vals <- sequence [do
-		val <- getColPrim i
-		return (v, val)
-			| (v, i) <- assocs vars]
-	return (obj, fromDistinctAscList vals)
+	(code, vars) <- doGLP opts lp
+	liftM (code, ) $ maybe (return Nothing) ( \ vars -> do
+		obj <- getObjVal
+		vals <- sequence [do
+			val <- getColPrim i
+			return (v, val)
+				| (v, i) <- assocs vars]
+		return (Just (obj, fromDistinctAscList vals))) vars
 glpSolveVars opts@MipOpts{} lp = runGLPK $ do
-	Just vars <- doGLP opts lp
-	obj <- mipObjVal
-	vals <- sequence [do
-		val <- mipColVal i
-		return (v, val)
-			| (v, i) <- assocs vars]
-	return (obj, fromDistinctAscList vals)
+	(code, vars) <- doGLP opts lp
+	liftM (code, ) $ maybe (return Nothing) (\ vars -> do
+		obj <- mipObjVal
+		vals <- sequence [do
+			val <- mipColVal i
+			return (v, val)
+				| (v, i) <- assocs vars]
+		return (Just (obj, fromDistinctAscList vals))) vars
 
 -- | Solves the linear or mixed integer programming problem.  Returns
 -- the value of the objective function, the values of the variables,
 -- and the values of any labeled rows.
-glpSolveAll :: (Ord v, Show v, Real c) => GLPOpts -> LP v c -> IO (Double, Map v Double, Map String Double)
+glpSolveAll :: (Ord v, Show v, Real c) => GLPOpts -> LP v c -> IO (ReturnCode, Maybe (Double, Map v Double, Map String Double))
 glpSolveAll opts@SimplexOpts{} lp@LP{..} = runGLPK $ do
-	Just vars <- doGLP opts lp
-	obj <- getObjVal
-	vals <- sequence [do
-		val <- getColPrim i
-		return (v, val)
-			| (v, i) <- assocs vars]
-	rows <- sequence [maybe (return Nothing) (\ nam -> do
-				val <- getRowPrim i
-				return (Just (nam, val))) nam
-				| (i, Constr nam _ _) <- zip [0..] constraints]
-	return (obj, fromDistinctAscList vals, fromDistinctAscList (catMaybes rows))
+	(code, vars) <- doGLP opts lp
+	liftM (code, ) $ maybe (return Nothing) (\ vars -> do
+		obj <- getObjVal
+		vals <- sequence [do
+			val <- getColPrim i
+			return (v, val)
+				| (v, i) <- assocs vars]
+		rows <- sequence [maybe (return Nothing) (\ nam -> do
+					val <- getRowPrim i
+					return (Just (nam, val))) nam
+					| (i, Constr nam _ _) <- zip [0..] constraints]
+		return (Just (obj, fromDistinctAscList vals, fromDistinctAscList (catMaybes rows)))) vars
 glpSolveAll opts@MipOpts{} lp@LP{..} = runGLPK $ do
-	Just vars <- doGLP opts lp
-	obj <- mipObjVal
-	vals <- sequence [do
-		val <- mipColVal i
-		return (v, val)
-			| (v, i) <- assocs vars]
-	rows <- sequence [maybe (return Nothing) (\ nam -> do
-				val <- mipRowVal i
-				return (Just (nam, val))) nam
-				| (i, Constr nam _ _) <- zip [0..] constraints]
-	return (obj, fromDistinctAscList vals, fromDistinctAscList (catMaybes rows))
+	(code, vars) <- doGLP opts lp
+	liftM (code, ) $ maybe (return Nothing) (\ vars -> do
+		obj <- mipObjVal
+		vals <- sequence [do
+			val <- mipColVal i
+			return (v, val)
+				| (v, i) <- assocs vars]
+		rows <- sequence [maybe (return Nothing) (\ nam -> do
+					val <- mipRowVal i
+					return (Just (nam, val))) nam
+					| (i, Constr nam _ _) <- zip [0..] constraints]
+		return (Just (obj, fromDistinctAscList vals, fromDistinctAscList (catMaybes rows)))) vars
 
-doGLP :: (Ord v, Show v, Real c) => GLPOpts -> LP v c -> GLPK (Maybe (Map v Int))
+doGLP :: (Ord v, Show v, Real c) => GLPOpts -> LP v c -> GLPK (ReturnCode, Maybe (Map v Int))
 doGLP SimplexOpts{..} lp = do
 	vars <- writeProblem lp
 	success <- solveSimplex msgLev tmLim presolve
-	return (Just vars)
+	return (success, guard (gaveAnswer success) >> Just vars)
 doGLP MipOpts{..} lp = do
 	vars <- writeProblem lp
 -- 	time <- getTime
@@ -95,7 +100,7 @@
 -- 	time' <- getTime
 	let tmLim' = tmLim  --- round (toRational (time' `diffUTCTime` time))
 	success <- mipSolve msgLev brTech btTech ppTech fpHeur cuts mipGap (fromIntegral tmLim') presolve
-	return (Just vars) --(if success then Just vars else Nothing)
+	return (success, guard (gaveAnswer success) >> Just vars) --(if success then Just vars else Nothing)
 -- 	where	getTime = liftIO getCurrentTime
 
 writeProblem :: (Ord v, Show v, Real c) => LP v c -> GLPK (Map v Int)
diff --git a/Data/LinearProgram/GLPK/Internal.hs b/Data/LinearProgram/GLPK/Internal.hs
--- a/Data/LinearProgram/GLPK/Internal.hs
+++ b/Data/LinearProgram/GLPK/Internal.hs
@@ -1,6 +1,6 @@
 {-# LANGUAGE ScopedTypeVariables, EmptyDataDecls, ForeignFunctionInterface #-}
 module Data.LinearProgram.GLPK.Internal (GLPK, MsgLev (..), Preprocessing (..), Direction(..), BacktrackTechnique(..),
-	BranchingTechnique(..), Cuts(..), runGLPK, writeLP, addCols,
+	BranchingTechnique(..), Cuts(..), ReturnCode(..), gaveAnswer, runGLPK, writeLP, addCols,
 	addRows, createIndex, findCol, findRow, getColPrim, getRowPrim, getObjVal,
 	mipColVal, mipRowVal, mipObjVal, mipSolve, setColBounds, setColKind, setColName, setMatRow,
 	setObjCoef, setObjectiveDirection, setRowBounds, setRowName, solveSimplex) where
@@ -21,6 +21,15 @@
 
 data GlpProb
 
+data ReturnCode = Success | InvalidBasis | SingularMatrix | IllConditionedMatrix | 
+	InvalidBounds | SolverFailed | ObjLowerLimReached | ObjUpperLimReached | 
+	IterLimReached | TimeLimReached | NoPrimalFeasible | NoDualFeasible | RootLPOptMissing |
+	SearchTerminated | MipGapTolReached | NoPrimDualFeasSolution | NoConvergence |
+	NumericalInstability | InvalidData | ResultOutOfRange deriving (Eq, Show, Enum)
+
+gaveAnswer :: ReturnCode -> Bool
+gaveAnswer = flip elem [Success, IterLimReached, TimeLimReached, SearchTerminated, MipGapTolReached]
+
 foreign import ccall unsafe "c_glp_create_prob" glpCreateProb :: IO (Ptr GlpProb)
 -- foreign import ccall "c_glp_set_obj_name" glpSetObjName :: Ptr GlpProb -> CString -> IO ()
 foreign import ccall unsafe "c_glp_set_obj_dir" glpSetObjDir :: Ptr GlpProb -> CInt -> IO ()
@@ -120,8 +129,8 @@
 
 data MsgLev = MsgOff | MsgErr | MsgOn | MsgAll
 
-solveSimplex :: MsgLev -> Int -> Bool -> GLPK Bool
-solveSimplex msglev tmLim presolve = GLP $ \ lp -> liftM (== 0) $ glpSolveSimplex lp
+solveSimplex :: MsgLev -> Int -> Bool -> GLPK ReturnCode
+solveSimplex msglev tmLim presolve = GLP $ \ lp -> liftM (toEnum . fromIntegral) $ glpSolveSimplex lp
 	(getMsgLev msglev)
 	tmLim'
 	(if presolve then 1 else 0)
@@ -155,9 +164,9 @@
 data Cuts = GMI | MIR | Cov | Clq deriving (Eq)
 
 mipSolve :: MsgLev -> BranchingTechnique -> BacktrackTechnique -> Preprocessing -> Bool ->
-	[Cuts] -> Double -> Int -> Bool -> GLPK Bool
+	[Cuts] -> Double -> Int -> Bool -> GLPK ReturnCode
 mipSolve msglev brt btt pp fp cuts mipgap tmlim presol =
-		liftM (== 0) $ GLP $ \ lp -> glpMipSolve lp msglev'
+		liftM (toEnum . fromIntegral) $ GLP $ \ lp -> glpMipSolve lp msglev'
 						brt' btt' pp' fp' tmlim' cuts' mipgap' presol'
 	where	!msglev' = getMsgLev msglev
 		!brt' = case brt of
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:        0.0.1
+Version:        0.0.2
 Author:         Louis Wasserman
 License:        GPL
 License-file:   LICENSE