Error: change type of handleError.

It now lives in IO and gives a proper message + exit
instead of calling 'error'.

We shouldn't be making it easier for people to raise error on
pure code.  And this is better for the main application
in IO.

3 files changed, 15 insertions, 16 deletions

diff --git a/src/Text/Pandoc.hs b/src/Text/Pandoc.hs
index 320af805a..4990a77fe 100644
--- a/src/Text/Pandoc.hs
+++ b/src/Text/Pandoc.hs
@@ -38,12 +38,11 @@ inline links:
 > module Main where
 > import Text.Pandoc
 >
-> markdownToRST :: String -> String
+> markdownToRST :: String -> Either PandocError String
 > markdownToRST =
->   writeRST def {writerReferenceLinks = True} .
->   handleError . readMarkdown def
+>   writeRST def {writerReferenceLinks = True} . readMarkdown def
 >
-> main = getContents >>= putStrLn . markdownToRST
+> main = getContents >>= either error return markdownToRST >>= putStrLn
 
 Note:  all of the readers assume that the input text has @'\n'@
 line endings.  So if you get your input text from a web form,
diff --git a/src/Text/Pandoc/Class.hs b/src/Text/Pandoc/Class.hs
index 7227742b2..8d3a73d08 100644
--- a/src/Text/Pandoc/Class.hs
+++ b/src/Text/Pandoc/Class.hs
@@ -190,7 +190,7 @@ withWarningsToStderr f = do
   return x
 
 runIOorExplode :: PandocIO a -> IO a
-runIOorExplode ma = handleError <$> runIO ma
+runIOorExplode ma = runIO ma >>= handleError
 
 newtype PandocIO a = PandocIO {
   unPandocIO :: ExceptT PandocError (StateT CommonState IO) a
diff --git a/src/Text/Pandoc/Error.hs b/src/Text/Pandoc/Error.hs
index c001b279a..f76749a80 100644
--- a/src/Text/Pandoc/Error.hs
+++ b/src/Text/Pandoc/Error.hs
@@ -35,6 +35,7 @@ import Text.Parsec.Error
 import Text.Parsec.Pos hiding (Line)
 import Data.Generics (Typeable)
 import Control.Exception (Exception)
+import Text.Pandoc.Shared (err)
 
 type Input = String
 
@@ -54,15 +55,15 @@ data PandocError = PandocFileReadError FilePath
 
 instance Exception PandocError
 
--- | An unsafe method to handle `PandocError`s.
-handleError :: Either PandocError a -> a
-handleError (Right r) = r
-handleError (Left err) =
-  case err of
-    PandocFileReadError fp -> error $ "problem reading " ++ fp
-    PandocShouldNeverHappenError s -> error s
-    PandocSomeError s -> error s
-    PandocParseError s -> error s
+-- | Handle PandocError by exiting with an error message.
+handleError :: Either PandocError a -> IO a
+handleError (Right r) = return r
+handleError (Left e) =
+  case e of
+    PandocFileReadError fp -> err 61 $ "problem reading " ++ fp
+    PandocShouldNeverHappenError s -> err 62 s
+    PandocSomeError s -> err 63 s
+    PandocParseError s -> err 64 s
     PandocParsecError input err' ->
         let errPos = errorPos err'
             errLine = sourceLine errPos
@@ -73,6 +74,5 @@ handleError (Left err) =
                                         ,"\n", replicate (errColumn - 1) ' '
                                         ,"^"]
                         else ""
-        in  error $ "\nError at " ++ show  err'
-                ++ errorInFile
+        in  err 65 $ "\nError at " ++ show  err' ++ errorInFile