readSource: handle errors internally

So the user does not have to.

src/Rib/Shake.hs

@@ -67,17 +67,20 @@ buildStaticFiles staticFilePatterns = do
 readSource ::
   SourceReader repr ->
   Path Rel File ->
-  Action (Either Text (Source repr))
-readSource r k = do
-  input <- ribInputDir
-  let f = input </> k
+  Action (Source repr)
+readSource sourceReader k = do
+  f <- (</> k) <$> ribInputDir
   -- NOTE: We don't really use cacheActionWith prior to parsing content,
   -- because the parsed representation (`repr`) may not always have instances
   -- for Typeable/Binary/Generic (for example, MMark does not expose its
   -- structure.). Consequently we are forced to cache merely the HTML writing
   -- stage (see buildHtml').
   need [toFilePath f]
-  fmap (Source k) <$> r f
+  sourceReader f >>= \case
+    Left e ->
+      fail $ "Error parsing source " <> toFilePath k <> ": " <> show e
+    Right v ->
+      pure $ Source k v
 
 -- | Convert the given pattern of source files into their HTML.
 buildHtmlMulti ::
@@ -92,14 +95,11 @@ buildHtmlMulti ::
 buildHtmlMulti pats parser r = do
   input <- ribInputDir
   fs <- getDirectoryFiles' input pats
-  forP fs $ \k ->
-    readSource parser k >>= \case
-      Left e ->
-        fail $ "Error parsing source " <> toFilePath k <> ": " <> show e
-      Right src -> do
-        outfile <- liftIO $ replaceExtension ".html" k
-        writeFileCached outfile $ toString $ Lucid.renderText $ r src
-        pure src
+  forP fs $ \k -> do
+    src <- readSource parser k
+    outfile <- liftIO $ replaceExtension ".html" k
+    writeFileCached outfile $ toString $ Lucid.renderText $ r src
+    pure src
 
 -- | Build a single HTML file with the given HTML value
 --