doc updates in System.IO

[ghc-base.git] / GHC / IO / Handle.hs

diff --git a/GHC/IO/Handle.hs b/GHC/IO/Handle.hs
index ff37738..bf706e0 100644 (file)
--- a/GHC/IO/Handle.hs
+++ b/GHC/IO/Handle.hs
@@ -393,6 +393,8 @@ hSetPosn (HandlePosn h i) = hSeek h AbsoluteSeek i
 --
 -- This operation may fail with:
 --
+--  * 'isIllegalOperationError' if the Handle is not seekable, or does
+--    not support the requested seek mode.
 --  * 'isPermissionError' if a system resource limit would be exceeded.
 
 hSeek :: Handle -> SeekMode -> Integer -> IO () 
@@ -417,6 +419,15 @@ hSeek handle mode offset =
     IODevice.seek haDevice mode offset
 
 
+-- | Computation 'hTell' @hdl@ returns the current position of the
+-- handle @hdl@, as the number of bytes from the beginning of
+-- the file.  The value returned may be subsequently passed to
+-- 'hSeek' to reposition the handle to the current position.
+-- 
+-- This operation may fail with:
+--
+--  * 'isIllegalOperationError' if the Handle is not seekable.
+--
 hTell :: Handle -> IO Integer
 hTell handle = 
     wantSeekableHandle "hGetPosn" handle $ \ handle_@Handle__{..} -> do