diff --git a/Cake/Core.hs b/Cake/Core.hs
--- a/Cake/Core.hs
+++ b/Cake/Core.hs
@@ -20,7 +20,7 @@
   distill,
   fileStamp,
   cut,
-  shielded,
+  -- shielded,
   Question(..),
   Answer(..),
   Failure(..),
@@ -30,7 +30,6 @@
   ) where
 
 import Data.Digest.Pure.MD5
--- import Data.Digest.OpenSSL.MD5 -- "nano-md5" -- md5sum
 
 import qualified Data.ByteString.Lazy as B
 import System.Directory
@@ -59,8 +58,18 @@
               deriving (Eq, Ord)
 $( derive makeBinary ''Question )             
                          
+data Failure = CakeError String | Panic | ProcessError ExitCode
+             deriving (Eq)
+instance Show Failure where
+  show (CakeError x) = x
+  show (ProcessError code) = "Process returned exit code " ++ show code
+  show (Panic) = "PANIC"
+$( derive makeBinary ''ExitCode )                                  
+$( derive makeBinary ''Failure )             
+
 data Answer = Stamp (Maybe MD5Digest) 
             | Text [String]
+            | Failed Failure
             deriving (Eq, Show)
 $( derive makeBinary ''Answer )             
 
@@ -78,7 +87,6 @@
 type Rule = P (Act ()) 
 type State = (Produced,Status)
 type Written = Dual DB -- take the dual so the writer overwrites old entries in the DB.
-data Failure = CakeError String | Panic | ProcessError ExitCode
 data Context = Context {ctxHandle :: Handle, ctxRule :: Rule, ctxDB :: DB, ctxProducing :: [Question]}
 newtype Act a = Act (ErrorT Failure (RWST Context Written State IO) a)
   deriving (Functor, Applicative, Monad, MonadIO, MonadState State, MonadWriter Written, MonadReader Context, MonadError Failure)
@@ -90,11 +98,6 @@
    noMsg = Panic
    strMsg = CakeError                  
 
-instance Show Failure where
-  show (CakeError x) = x
-  show (ProcessError code) = "Process returned exit code " ++ show code
-  show (Panic) = "PANIC"
-
 instance Applicative P where
   (<*>) = ap
   pure = return
@@ -119,7 +122,8 @@
   oldDB <- if e 
     then decodeFile databaseFile
     else return $ M.empty
-  newDB <- runAct rule oldDB action
+  newAnswers <- runAct rule oldDB action
+  let newDB = newAnswers <> oldDB -- new answers overwrite old ones
   putStrLn $ "Database is:"
   forM_ (M.assocs newDB) $ \(k,v) ->
     putStrLn $ (show k) ++ " => " ++ (show v)
@@ -131,30 +135,33 @@
   (ps,_) <- RWS.get
   return $ f `S.member` ps
 
+modCx q (Context {..}) = Context {ctxProducing = q:ctxProducing,..}    
+
 -- | Answer a question using the action given.
--- The action should be independent of the context.
+-- The action must be independent of the context.
 distill :: Question -> Act Answer -> Act Answer
-distill q act = 
-  local (modCx q) $ do
-    debug $ "Starting to answer"
-    db <- ctxDB <$> ask
-    let a0 = M.lookup q db
-    a1 <- shielded act
-    tell (Dual $ M.singleton q a1)
-    when (Just a1 /= a0) $ do
-      clobber
-      debug $ "Question has not the same answer"
-    return a1
-
-modCx q (Context {..}) = Context {ctxProducing = q:ctxProducing,..}    
+distill q act = local (modCx q) $ do
+  debug $ "Starting to answer"
+  db <- ctxDB <$> ask
+  a1 <- refresh q act
+  when (Just a1 /= M.lookup q db) $ do
+    clobber
+    debug $ "Question has not the same answer"
+  return a1
 
+-- | Answer a question using the action given. The action must be
+-- independent of the context. The result is not compared to the
+-- previous run, so it is the caller responsibility that the new
+-- answer is properly taken into account.
 refresh :: Question -> Act Answer -> Act Answer
-refresh q act = local (modCx q) $ do
-   debug $ "Overwriting"
-   a <- shielded act
-   tell (Dual $ M.singleton q a)
-   return a
-   
+refresh q act = 
+  do a <- shielded act
+     tell (Dual $ M.singleton q a)
+     return a
+  `catchError` \ e -> do -- on error
+     tell (Dual $ M.singleton q $ Failed e) -- Answering the question failed...
+     throwError e -- and questions depending on it will also fail
+
 -- | Produce a file, using the given action.
 -- The action should be independent of the context.
 produce :: FilePath -> Act () -> Act ()
@@ -187,7 +194,7 @@
 
 
 -- | Mark that a file is used. Do not chase dependencies on this file
--- though.
+-- though. (To be used eg. if a command uses an optional file).
 use f = distill (FileContents f) (fileStamp f)
 
 
diff --git a/Cake/Rules.hs b/Cake/Rules.hs
--- a/Cake/Rules.hs
+++ b/Cake/Rules.hs
@@ -50,7 +50,10 @@
 pandoc inp typ options = produce out $ do 
   need inp
   cut $ system $ ["pandoc",inp,"-t",typ,"-o",out] ++ options
- where out = replaceExtension inp typ
+ where out = replaceExtension inp ext
+       ext = case typ of 
+               "latex" -> "tex"
+               _ -> typ
  
 graphviz program inp typ options = produce out $ needing [inp] $ do
   system $ [program, "-T"++typ, "-o"++out, inp] ++ options
@@ -79,7 +82,7 @@
   
 
 tex_markdown_standalone = simple ".tex" ".markdown" $ \o i -> 
-  pandoc i o ["--standalone"]
+  pandoc i "latex" ["--standalone"]
 {-
 html_markdown_standalone = simple ".html" ".markdown" $ \o i -> 
   system ["pandoc","--tab-stop=2","--standalone","-f","markdown","-t","latex", 
diff --git a/cake.cabal b/cake.cabal
--- a/cake.cabal
+++ b/cake.cabal
@@ -1,5 +1,5 @@
 name:           cake
-version:        0.4.0.0
+version:        0.4.2.0
 category:       Development
 synopsis:       A build-system library and driver
 description:
@@ -21,9 +21,9 @@
   build-depends: filepath==1.3.*  
   build-depends: process==1.1.*
   build-depends: binary==0.5.*
-  build-depends: containers==0.4.*
-  build-depends: directory==1.1.*
-  build-depends: bytestring==0.9.*
+  build-depends: containers==0.5.*
+  build-depends: directory==1.2.*
+  build-depends: bytestring==0.10.*
   build-depends: pureMD5==2.1.*
   build-depends: split==0.1.*
 
@@ -37,7 +37,7 @@
   build-depends: regex-tdfa==1.1.*
   build-depends: array==0.4.*
   build-depends: filepath==1.3.*  
-  build-depends: directory==1.1.*
+  build-depends: directory==1.2.*
 
   main-is: Main.hs