From a45394a21c65860e30782278562b0a8e1a8b0190 Mon Sep 17 00:00:00 2001
From: Joachim Fasting <joachim.fasting@gmail.com>
Date: Wed, 5 Mar 2008 18:20:02 +0000
Subject: [PATCH] [gitconv @ N.M.Commands.plChangesPosId: reimplement with
 error checking] Uses PatternGuards because not using them was seriously
 clunky.

---
 Network/MPD/Commands.hs | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/Network/MPD/Commands.hs b/Network/MPD/Commands.hs
index 3d0b2b6..66eb4e1 100644
--- a/Network/MPD/Commands.hs
+++ b/Network/MPD/Commands.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE PatternGuards #-}
 {-
     libmpd for Haskell, an MPD client library.
     Copyright (C) 2005-2008  Ben Sinclair <bsinclai@turing.une.edu.au>
@@ -22,7 +23,7 @@
 -- License     : LGPL
 -- Maintainer  : bsinclai@turing.une.edu.au
 -- Stability   : alpha
--- Portability : Haskell 98
+-- Portability : unportable (uses PatternGuards)
 --
 -- Interface to the user commands supported by MPD.
 
@@ -399,9 +400,12 @@ plChanges version =
 -- | Like 'plChanges' but only returns positions and ids.
 plChangesPosId :: Integer -> MPD [(PLIndex, PLIndex)]
 plChangesPosId plver =
-    liftM (map takePosid . splitGroups . toAssoc) (getResponse cmd)
-    where cmd          = "plchangesposid " ++ show plver
-          takePosid xs = (Pos $ takeNum "cpos" xs, ID $ takeNum "Id" xs)
+    getResponse ("plchangesposid " ++ show plver) >>=
+    mapM f . splitGroups . toAssoc
+    where f xs | [("cpos", x), ("Id", y)] <- xs
+               , Just (x', y') <- pair parseNum (x, y)
+               = return (Pos x', ID y')
+               | otherwise = throwError . Unexpected $ show xs
 
 -- | Search for songs in the current playlist with strict matching.
 playlistFind :: Query -> MPD [Song]
-- 
2.11.4.GIT