Make benchmarks compile again.

Additionally, fix the problem which caused one failing benchmark
to stop other benchmarks from running.

benchmark/benchmark-pandoc.hs

@@ -20,19 +20,20 @@ import Criterion.Main
 import Criterion.Config
 import System.Environment (getArgs)
 import Data.Monoid
+import Data.Maybe (mapMaybe)
+import Debug.Trace (trace)
 
 readerBench :: Pandoc
             -> (String, ReaderOptions -> String -> IO Pandoc)
-            -> Benchmark
-readerBench doc (name, reader) =
-  let writer = case lookup name writers of
-                     Just (PureStringWriter w) -> w
-                     _ -> error $ "Could not find writer for " ++ name
-      inp = writer def{ writerWrapText = True } doc
+            -> Maybe Benchmark
+readerBench doc (name, reader) = case lookup name writers of
+  Just (PureStringWriter writer) ->
+    let inp = writer def{ writerWrapText = True} doc
         -- we compute the length to force full evaluation
         getLength (Pandoc (Meta _) d) = length d
-  in  bench (name ++ " reader") $ whnfIO $ getLength `fmap`
+    in return $ bench (name ++ " reader") $ whnfIO $ getLength `fmap`
                  (reader def{ readerSmart = True }) inp
+  _ -> trace ("\nCould not find writer for " ++ name ++ "\n") Nothing
 
 writerBench :: Pandoc
             -> (String, WriterOptions -> Pandoc -> String)
@@ -43,13 +44,17 @@ writerBench doc (name, writer) = bench (name ++ " writer") $ nf
 main :: IO ()
 main = do
   args <- getArgs
-  (conf,_) <- parseArgs defaultConfig{ cfgSamples = Last $ Just 20 }  defaultOptions args
+  (conf,_) <- parseArgs defaultConfig{ cfgSamples = Last $ Just 20 }
+                        defaultOptions args
   inp <- readFile "README"
   inp2 <- readFile "tests/testsuite.txt"
   let opts = def{ readerSmart = True }
   let doc = readMarkdown opts $ inp ++ unlines (drop 3 $ lines inp2)
-  let readerBs = map (readerBench doc)
-                 $ filter (\(n,_) -> n /="haddock") readers
+  let readers' = [(n,r) | (n, StringReader r) <- readers]
+  let readerBs = mapMaybe (readerBench doc)
+                 $ filter (\(n,_) -> n /="haddock") readers'
   let writers' = [(n,w) | (n, PureStringWriter w) <- writers]
+  let writerBs = map (writerBench doc)
+                 $ writers'
   defaultMainWith conf (return ()) $
-    map (writerBench doc) writers' ++ readerBs
+    writerBs ++ readerBs