Network/MPD/Utils.hs

   1 {-
   2     libmpd for Haskell, an MPD client library.
   3     Copyright (C) 2005-2008  Ben Sinclair <bsinclai@turing.une.edu.au>
   4
   5     This library is free software; you can redistribute it and/or
   6     modify it under the terms of the GNU Lesser General Public
   7     License as published by the Free Software Foundation; either
   8     version 2.1 of the License, or (at your option) any later version.
   9
  10     This library is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13     Lesser General Public License for more details.
  14
  15     You should have received a copy of the GNU Lesser General Public
  16     License along with this library; if not, write to the Free Software
  17     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  18 -}
  19
  20 -- | Module    : Network.MPD.Utils
  21 -- Copyright   : (c) Ben Sinclair 2005-2008
  22 -- License     : LGPL
  23 -- Maintainer  : bsinclai@turing.une.edu.au
  24 -- Stability   : alpha
  25 -- Portability : Haskell 98
  26 --
  27 -- Utilities.
  28
  29 module Network.MPD.Utils (
  30     parseNum, parseBool, showBool,
  31     toAssoc, splitGroups
  32     ) where
  33
  34 -- Parse a positive or negative integer value, returning 'Nothing' on failure.
  35 parseNum :: (Read a, Integral a) => String -> Maybe a
  36 parseNum s = do
  37     [(x, "")] <- return (reads s)
  38     return x
  39
  40 -- Inverts 'parseBool'.
  41 showBool :: Bool -> String
  42 showBool x = if x then "1" else "0"
  43
  44 -- Parse a boolean response value.
  45 parseBool :: String -> Bool
  46 parseBool = (== "1") . take 1
  47
  48 -- Break up a list of strings into an assoc. list, separating at
  49 -- the first ':'.
  50 toAssoc :: [String] -> [(String, String)]
  51 toAssoc = map f
  52     where f x = let (k,v) = break (== ':') x in
  53                 (k,dropWhile (== ' ') $ drop 1 v)
  54
  55 -- Takes an assoc. list with recurring keys, and groups each cycle of
  56 -- keys with their values together. The first key of each cycle needs
  57 -- to be present in every cycle for it to work, but the rest don't
  58 -- affect anything.
  59 --
  60 -- > splitGroups [(1,'a'),(2,'b'),(1,'c'),(2,'d')] ==
  61 -- >     [[(1,'a'),(2,'b')],[(1,'c'),(2,'d')]]
  62 splitGroups :: Eq a => [(a, b)] -> [[(a, b)]]
  63 splitGroups [] = []
  64 splitGroups (x:xs) = ((x:us):splitGroups vs)
  65     where (us,vs) = break (\y -> fst x == fst y) xs