Documentation improvements and cleanup relating to the IOE monad

Renamed appIOE to tryIOE (it is analogous to 'try' in the standard libraries).
Removed unused IOE operations & documented the remaining ones.
Removed/simplified superfluous uses of IOE operations.

6 files changed, 22 insertions, 24 deletions

diff --git a/src/compiler/GF/Command/Importing.hs b/src/compiler/GF/Command/Importing.hs
index e2284aa58..4ef966f77 100644
--- a/src/compiler/GF/Command/Importing.hs
+++ b/src/compiler/GF/Command/Importing.hs
@@ -10,7 +10,7 @@ import GF.Grammar (SourceGrammar) -- for cc command
 import GF.Grammar.CFG
 import GF.Grammar.EBNF
 import GF.Compile.CFGtoPGF
-import GF.Infra.UseIO
+import GF.Infra.UseIO(die,tryIOE,useIOE)
 import GF.Infra.Option
 import GF.Data.ErrM
 
@@ -29,7 +29,7 @@ importGrammar pgf0 opts files =
       let cs = concatMap snd ascss
       importGrammar pgf0 opts cs
     s | elem s [".gf",".gfo"] -> do
-      res <- appIOE $ compileToPGF opts files
+      res <- tryIOE $ compileToPGF opts files
       case res of
         Ok pgf2 -> ioUnionPGF pgf0 pgf2
         Bad msg -> do putStrLn ('\n':'\n':msg)
@@ -46,19 +46,10 @@ ioUnionPGF one two = case msgUnionPGF one two of
 
 importSource :: SourceGrammar -> Options -> [FilePath] -> IO SourceGrammar
 importSource src0 opts files = do
-  src <- appIOE $ batchCompile opts files
-  case src of
-    Ok (_,(_,gr)) -> return gr
-    Bad msg -> do 
-      putStrLn msg
-      return src0
+  useIOE src0 (fmap (snd.snd) (batchCompile opts files))
 
 -- for different cf formats
-importCF opts files get convert = do
-  res <- appIOE impCF
-  case res of
-    Ok pgf -> return pgf
-    Bad s  -> error s
+importCF opts files get convert = impCF
   where
     impCF = do
       rules <- fmap (convert . concat) $ mapM (get opts) files
@@ -66,6 +57,6 @@ importCF opts files get convert = do
                     (CFRule cat _ _ : _) -> return cat
                     _                    -> fail "empty CFG"
       let pgf = cf2pgf (last files) (uniqueFuns (mkCFG startCat Set.empty rules))
-      probs <- liftIO (maybe (return . defaultProbabilities) readProbabilitiesFromFile (flag optProbsFile opts) pgf)
+      probs <- maybe (return . defaultProbabilities) readProbabilitiesFromFile (flag optProbsFile opts) pgf
       return $ setProbabilities probs 
              $ if flag optOptimizePGF opts then optimizePGF pgf else pgf
diff --git a/src/compiler/GF/CompileInParallel.hs b/src/compiler/GF/CompileInParallel.hs
index 22a53a841..48e5821b0 100644
--- a/src/compiler/GF/CompileInParallel.hs
+++ b/src/compiler/GF/CompileInParallel.hs
@@ -81,11 +81,11 @@ batchCompile1 lib_dir (opts,filepaths) =
                          takeFileName f `elem` prelude_files
          ppPath ps = "-path="<>intercalate ":" (map rel ps)
      deps <- newMVar M.empty
-     toLog <- newLog runIOE
+     toLog <- newLog id
      term <- getTermColors
      let --logStrLn = toLog . ePutStrLn
        --ok :: CollectOutput IO a -> IO a
-         ok (CO m) = err bad good =<< appIOE m
+         ok (CO m) = err bad good =<< tryIOE m
            where
               good (o,r) = do toLog o; return r
               bad e = do toLog (redPutStrLn e); fail "failed"
@@ -98,7 +98,7 @@ batchCompile1 lib_dir (opts,filepaths) =
 --            logStrLn $ "Finished "++show (length (modules gr'))++" modules."
               return gr'
      fcache <- liftIO $ newIOCache $ \ _ (imp,Hide (f,ps)) ->
-                 do (file,_,_) <- runIOE $ findFile gfoDir ps imp
+                 do (file,_,_) <- findFile gfoDir ps imp
                     return (file,(f,ps))
      let find f ps imp =
            do (file',(f',ps')) <- liftIO $ readIOCache fcache (imp,Hide (f,ps))
diff --git a/src/compiler/GF/Compiler.hs b/src/compiler/GF/Compiler.hs
index d92ed387c..57855b1b9 100644
--- a/src/compiler/GF/Compiler.hs
+++ b/src/compiler/GF/Compiler.hs
@@ -28,7 +28,7 @@ import Control.Monad(unless,forM_)
 -- and, depending on the options, a @.pgf@ file. (@gf -batch@, @gf -make@)
 mainGFC :: Options -> [FilePath] -> IO ()
 mainGFC opts fs = do
-  r <- appIOE (case () of
+  r <- tryIOE (case () of
                  _ | null fs -> fail $ "No input files."
                  _ | all (extensionIs ".cf")  fs -> compileCFFiles opts fs
                  _ | all (\f -> extensionIs ".gf" f || extensionIs ".gfo" f)  fs -> compileSourceFiles opts fs
diff --git a/src/compiler/GF/Infra/UseIO.hs b/src/compiler/GF/Infra/UseIO.hs
index b5ef38f49..14120d811 100644
--- a/src/compiler/GF/Infra/UseIO.hs
+++ b/src/compiler/GF/Infra/UseIO.hs
@@ -129,14 +129,16 @@ splitInModuleSearchPath s = case break isPathSep s of
 -- | Was: @newtype IOE a = IOE { appIOE :: IO (Err a) }@
 type IOE a = IO a
 
-ioe :: IO (Err a) -> IOE a
-ioe io = err fail return =<< io
+--ioe :: IO (Err a) -> IOE a
+--ioe io = err fail return =<< io
 
-appIOE :: IOE a -> IO (Err a)
-appIOE ioe = handle (fmap Ok ioe) (return . Bad)
+-- | Catch exceptions caused by calls to 'raise' or 'fail' in the 'IO' monad.
+-- To catch all 'IO' exceptions, use 'try' instead.
+tryIOE :: IOE a -> IO (Err a)
+tryIOE ioe = handle (fmap Ok ioe) (return . Bad)
 
-runIOE :: IOE a -> IO a
-runIOE = id
+--runIOE :: IOE a -> IO a
+--runIOE = id
 
 -- instance MonadIO IOE where liftIO io = ioe (io >>= return . return)
 
@@ -160,6 +162,8 @@ instance  Monad IOE where
                   appIOE $ err raise f x         -- f :: a -> IOE a
   fail = raise
 -}
+
+-- | Print the error message and return a default value if the IO operation 'fail's
 useIOE :: a -> IOE a -> IO a
 useIOE a ioe = handle ioe (\s -> putStrLn s >> return a)
 
diff --git a/src/compiler/GF/Support.hs b/src/compiler/GF/Support.hs
index a4baf63c9..dfab662ea 100644
--- a/src/compiler/GF/Support.hs
+++ b/src/compiler/GF/Support.hs
@@ -4,6 +4,7 @@ module GF.Support(
            module GF.Infra.Option,
            module GF.Data.Operations,
            module GF.Infra.UseIO,
+           module GF.System.Catch,
            module GF.System.Console,
            -- ** Binary serialisation
            Binary,encode,decode,encodeFile,decodeFile
@@ -13,5 +14,6 @@ import GF.Infra.Location
 import GF.Data.Operations
 import GF.Infra.Option
 import GF.Infra.UseIO
+import GF.System.Catch
 import GF.System.Console
 import Data.Binary
diff --git a/src/compiler/GF/System/Catch.hs b/src/compiler/GF/System/Catch.hs
index 950774947..f69934af5 100644
--- a/src/compiler/GF/System/Catch.hs
+++ b/src/compiler/GF/System/Catch.hs
@@ -3,6 +3,7 @@
 module GF.System.Catch where
 import qualified System.IO.Error as S
 
+-- ** Backwards compatible try and catch
 #if MIN_VERSION_base(4,4,0)
 catch = S.catchIOError
 try = S.tryIOError