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     parseDate, parseNum, parseBool, showBool,
  31     breakChar, toAssoc, splitGroups
  32     ) where
  33
  34 import Data.Char (isDigit)
  35
  36 -- Break a string a character, removing the separator.
  37 breakChar :: Char -> String -> (String, String)
  38 breakChar c s = let (x, y) = break (== c) s in (x, drop 1 y)
  39
  40 -- XXX: need a more robust date parser.
  41 -- Parse a date value.
  42 -- > parseDate "2008" = Just 2008
  43 -- > parseDate "2008-03-01" = Just 2008
  44 parseDate :: String -> Maybe Int
  45 parseDate = parseNum . takeWhile isDigit
  46
  47 -- Parse a positive or negative integer value, returning 'Nothing' on failure.
  48 parseNum :: (Read a, Integral a) => String -> Maybe a
  49 parseNum s = do
  50     [(x, "")] <- return (reads s)
  51     return x
  52
  53 -- Inverts 'parseBool'.
  54 showBool :: Bool -> String
  55 showBool x = if x then "1" else "0"
  56
  57 -- Parse a boolean response value.
  58 parseBool :: String -> Maybe Bool
  59 parseBool s = case take 1 s of
  60                   "1" -> Just True
  61                   "0" -> Just False
  62                   _   -> Nothing
  63
  64 -- Break up a list of strings into an assoc. list, separating at
  65 -- the first ':'.
  66 toAssoc :: [String] -> [(String, String)]
  67 toAssoc = map f
  68     where f x = let (k,v) = break (== ':') x in
  69                 (k,dropWhile (== ' ') $ drop 1 v)
  70
  71 -- Takes an assoc. list with recurring keys, and groups each cycle of
  72 -- keys with their values together. The first key of each cycle needs
  73 -- to be present in every cycle for it to work, but the rest don't
  74 -- affect anything.
  75 --
  76 -- > splitGroups [(1,'a'),(2,'b'),(1,'c'),(2,'d')] ==
  77 -- >     [[(1,'a'),(2,'b')],[(1,'c'),(2,'d')]]
  78 splitGroups :: Eq a => [(a, b)] -> [[(a, b)]]
  79 splitGroups [] = []
  80 splitGroups (x:xs) = ((x:us):splitGroups vs)
  81     where (us,vs) = break (\y -> fst x == fst y) xs