## root / src / Ganeti / Utils.hs @ ace37e24

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{-| Utility functions. -} |
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{- |

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Copyright (C) 2009, 2010, 2011, 2012, 2013 Google Inc. |

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This program is free software; you can redistribute it and/or modify |

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it under the terms of the GNU General Public License as published by |

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the Free Software Foundation; either version 2 of the License, or |

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(at your option) any later version. |

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This program is distributed in the hope that it will be useful, but |

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WITHOUT ANY WARRANTY; without even the implied warranty of |

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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |

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General Public License for more details. |

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You should have received a copy of the GNU General Public License |

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along with this program; if not, write to the Free Software |

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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |

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02110-1301, USA. |

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-} |

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module Ganeti.Utils |

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( debug |

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, debugFn |

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, debugXy |

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, sepSplit |

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, stdDev |

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, if' |

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, select |

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, applyIf |

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, commaJoin |

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, ensureQuoted |

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, tryRead |

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, formatTable |

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, printTable |

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, parseUnit |

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, plural |

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, niceSort |

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, niceSortKey |

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, exitIfBad |

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, exitErr |

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, exitWhen |

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, exitUnless |

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, rStripSpace |

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, newUUID |

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, getCurrentTime |

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, clockTimeToString |

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, chompPrefix |

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) where |

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import Data.Char (toUpper, isAlphaNum, isDigit, isSpace) |

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import Data.Function (on) |

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import Data.List |

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import Debug.Trace |

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import Ganeti.BasicTypes |

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import qualified Ganeti.Constants as C |

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import System.IO |

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import System.Exit |

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import System.Time |

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-- * Debug functions |

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-- | To be used only for debugging, breaks referential integrity. |

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debug :: Show a => a -> a |

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debug x = trace (show x) x |

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-- | Displays a modified form of the second parameter before returning |

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-- it. |

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debugFn :: Show b => (a -> b) -> a -> a |

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debugFn fn x = debug (fn x) `seq` x |

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-- | Show the first parameter before returning the second one. |

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debugXy :: Show a => a -> b -> b |

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debugXy = seq . debug |

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-- * Miscellaneous |

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-- | Apply the function if condition holds, otherwise use default value. |

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applyIf :: Bool -> (a -> a) -> a -> a |

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applyIf b f x = if b then f x else x |

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-- | Comma-join a string list. |

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commaJoin :: [String] -> String |

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commaJoin = intercalate "," |

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-- | Split a list on a separator and return an array. |

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sepSplit :: Eq a => a -> [a] -> [[a]] |

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sepSplit sep s |

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| null s = [] |

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| null xs = [x] |

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| null ys = [x,[]] |

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| otherwise = x:sepSplit sep ys |

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where (x, xs) = break (== sep) s |

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ys = drop 1 xs |

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-- | Simple pluralize helper |

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plural :: Int -> String -> String -> String |

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plural 1 s _ = s |

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plural _ _ p = p |

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-- | Ensure a value is quoted if needed. |

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ensureQuoted :: String -> String |

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ensureQuoted v = if not (all (\c -> isAlphaNum c || c == '.') v) |

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then '\'':v ++ "'" |

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else v |

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-- * Mathematical functions |

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-- Simple and slow statistical functions, please replace with better |

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-- versions |

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-- | Standard deviation function. |

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stdDev :: [Double] -> Double |

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stdDev lst = |

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-- first, calculate the list length and sum lst in a single step, |

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-- for performance reasons |

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let (ll', sx) = foldl' (\(rl, rs) e -> |

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let rl' = rl + 1 |

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rs' = rs + e |

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in rl' `seq` rs' `seq` (rl', rs')) (0::Int, 0) lst |

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ll = fromIntegral ll'::Double |

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mv = sx / ll |

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av = foldl' (\accu em -> let d = em - mv in accu + d * d) 0.0 lst |

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in sqrt (av / ll) -- stddev |

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-- * Logical functions |

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-- Avoid syntactic sugar and enhance readability. These functions are proposed |

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-- by some for inclusion in the Prelude, and at the moment they are present |

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-- (with various definitions) in the utility-ht package. Some rationale and |

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-- discussion is available at <http://www.haskell.org/haskellwiki/If-then-else> |

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-- | \"if\" as a function, rather than as syntactic sugar. |

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if' :: Bool -- ^ condition |

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-> a -- ^ \"then\" result |

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-> a -- ^ \"else\" result |

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-> a -- ^ \"then\" or "else" result depending on the condition |

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if' True x _ = x |

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if' _ _ y = y |

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-- * Parsing utility functions |

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-- | Parse results from readsPrec. |

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parseChoices :: (Monad m, Read a) => String -> String -> [(a, String)] -> m a |

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parseChoices _ _ ((v, ""):[]) = return v |

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parseChoices name s ((_, e):[]) = |

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fail $ name ++ ": leftover characters when parsing '" |

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++ s ++ "': '" ++ e ++ "'" |

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parseChoices name s _ = fail $ name ++ ": cannot parse string '" ++ s ++ "'" |

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-- | Safe 'read' function returning data encapsulated in a Result. |

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tryRead :: (Monad m, Read a) => String -> String -> m a |

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tryRead name s = parseChoices name s $ reads s |

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-- | Format a table of strings to maintain consistent length. |

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formatTable :: [[String]] -> [Bool] -> [[String]] |

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formatTable vals numpos = |

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let vtrans = transpose vals -- transpose, so that we work on rows |

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-- rather than columns |

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mlens = map (maximum . map length) vtrans |

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expnd = map (\(flds, isnum, ml) -> |

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map (\val -> |

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let delta = ml - length val |

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filler = replicate delta ' ' |

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in if delta > 0 |

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then if isnum |

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then filler ++ val |

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else val ++ filler |

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else val |

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) flds |

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) (zip3 vtrans numpos mlens) |

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in transpose expnd |

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-- | Constructs a printable table from given header and rows |

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printTable :: String -> [String] -> [[String]] -> [Bool] -> String |

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printTable lp header rows isnum = |

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unlines . map ((++) lp . (:) ' ' . unwords) $ |

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formatTable (header:rows) isnum |

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-- | Converts a unit (e.g. m or GB) into a scaling factor. |

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parseUnitValue :: (Monad m) => String -> m Rational |

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parseUnitValue unit |

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-- binary conversions first |

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| null unit = return 1 |

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| unit == "m" || upper == "MIB" = return 1 |

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| unit == "g" || upper == "GIB" = return kbBinary |

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| unit == "t" || upper == "TIB" = return $ kbBinary * kbBinary |

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-- SI conversions |

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| unit == "M" || upper == "MB" = return mbFactor |

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| unit == "G" || upper == "GB" = return $ mbFactor * kbDecimal |

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| unit == "T" || upper == "TB" = return $ mbFactor * kbDecimal * kbDecimal |

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| otherwise = fail $ "Unknown unit '" ++ unit ++ "'" |

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where upper = map toUpper unit |

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kbBinary = 1024 :: Rational |

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kbDecimal = 1000 :: Rational |

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decToBin = kbDecimal / kbBinary -- factor for 1K conversion |

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mbFactor = decToBin * decToBin -- twice the factor for just 1K |

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-- | Tries to extract number and scale from the given string. |

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-- |

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-- Input must be in the format NUMBER+ SPACE* [UNIT]. If no unit is |

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-- specified, it defaults to MiB. Return value is always an integral |

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-- value in MiB. |

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parseUnit :: (Monad m, Integral a, Read a) => String -> m a |

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parseUnit str = |

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-- TODO: enhance this by splitting the unit parsing code out and |

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-- accepting floating-point numbers |

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case (reads str::[(Int, String)]) of |

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[(v, suffix)] -> |

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let unit = dropWhile (== ' ') suffix |

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in do |

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scaling <- parseUnitValue unit |

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return $ truncate (fromIntegral v * scaling) |

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_ -> fail $ "Can't parse string '" ++ str ++ "'" |

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-- | Unwraps a 'Result', exiting the program if it is a 'Bad' value, |

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-- otherwise returning the actual contained value. |

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exitIfBad :: String -> Result a -> IO a |

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exitIfBad msg (Bad s) = exitErr (msg ++ ": " ++ s) |

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exitIfBad _ (Ok v) = return v |

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-- | Exits immediately with an error message. |

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exitErr :: String -> IO a |

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exitErr errmsg = do |

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hPutStrLn stderr $ "Error: " ++ errmsg |

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exitWith (ExitFailure 1) |

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-- | Exits with an error message if the given boolean condition if true. |

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exitWhen :: Bool -> String -> IO () |

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exitWhen True msg = exitErr msg |

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exitWhen False _ = return () |

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-- | Exits with an error message /unless/ the given boolean condition |

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-- if true, the opposite of 'exitWhen'. |

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exitUnless :: Bool -> String -> IO () |

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exitUnless cond = exitWhen (not cond) |

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-- | Helper for 'niceSort'. Computes the key element for a given string. |

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extractKey :: [Either Integer String] -- ^ Current (partial) key, reversed |

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-> String -- ^ Remaining string |

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-> ([Either Integer String], String) |

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extractKey ek [] = (reverse ek, []) |

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extractKey ek xs@(x:_) = |

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let (span_fn, conv_fn) = if isDigit x |

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then (isDigit, Left . read) |

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else (not . isDigit, Right) |

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(k, rest) = span span_fn xs |

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in extractKey (conv_fn k:ek) rest |

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{-| Sort a list of strings based on digit and non-digit groupings. |

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Given a list of names @['a1', 'a10', 'a11', 'a2']@ this function |

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will sort the list in the logical order @['a1', 'a2', 'a10', 'a11']@. |

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The sort algorithm breaks each name in groups of either only-digits or |

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no-digits, and sorts based on each group. |

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Internally, this is not implemented via regexes (like the Python |

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version), but via actual splitting of the string in sequences of |

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either digits or everything else, and converting the digit sequences |

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in /Left Integer/ and the non-digit ones in /Right String/, at which |

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point sorting becomes trivial due to the built-in 'Either' ordering; |

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we only need one extra step of dropping the key at the end. |

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-} |

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niceSort :: [String] -> [String] |

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niceSort = niceSortKey id |

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-- | Key-version of 'niceSort'. We use 'sortBy' and @compare `on` fst@ |

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-- since we don't want to add an ordering constraint on the /a/ type, |

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-- hence the need to only compare the first element of the /(key, a)/ |

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-- tuple. |

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niceSortKey :: (a -> String) -> [a] -> [a] |

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niceSortKey keyfn = |

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map snd . sortBy (compare `on` fst) . |

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map (\s -> (fst . extractKey [] $ keyfn s, s)) |

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-- | Strip space characthers (including newline). As this is |

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-- expensive, should only be run on small strings. |

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rStripSpace :: String -> String |

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rStripSpace = reverse . dropWhile isSpace . reverse |

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-- | Returns a random UUID. |

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-- This is a Linux-specific method as it uses the /proc filesystem. |

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newUUID :: IO String |

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newUUID = do |

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contents <- readFile C.randomUuidFile |

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return $! rStripSpace $ take 128 contents |

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-- | Returns the current time as an Integer representing the number of |

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-- seconds from the Unix epoch. |

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getCurrentTime :: IO Integer |

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getCurrentTime = do |

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TOD ctime _ <- getClockTime |

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return ctime |

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-- | Convert a ClockTime into a (seconds-only) timestamp. |

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clockTimeToString :: ClockTime -> String |

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clockTimeToString (TOD t _) = show t |

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{-| Strip a prefix from a string, allowing the last character of the prefix |

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(which is assumed to be a separator) to be absent from the string if the string |

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terminates there. |

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>>> chompPrefix "foo:bar:" "a:b:c" |

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Nothing |

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>>> chompPrefix "foo:bar:" "foo:bar:baz" |

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Just "baz" |

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>>> chompPrefix "foo:bar:" "foo:bar:" |

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Just "" |

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>>> chompPrefix "foo:bar:" "foo:bar" |

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Just "" |

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>>> chompPrefix "foo:bar:" "foo:barbaz" |

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Nothing |

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-} |

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chompPrefix :: String -> String -> Maybe String |

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chompPrefix pfx str = |

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if pfx `isPrefixOf` str || str == init pfx |

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then Just $ drop (length pfx) str |

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else Nothing |