## root / htools / Ganeti / HTools / Utils.hs @ 34ace266

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

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Copyright (C) 2009, 2010, 2011 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.HTools.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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, tryRead |

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, formatTable |

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, parseUnit |

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, plural |

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) where |

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import Data.Char (toUpper) |

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import Data.List |

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import Debug.Trace |

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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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-- * 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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-- | Return the first result with a True condition, or the default otherwise. |

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select :: a -- ^ default result |

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-> [(Bool, a)] -- ^ list of \"condition, result\" |

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-> a -- ^ first result which has a True condition, or default |

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select def = maybe def snd . find fst |

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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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-- | 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 of |

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[(v, suffix)] -> |

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

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upper = map toUpper unit |

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siConvert x = x * 1000000 `div` 1048576 |

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in case () of |

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_ | null unit -> return v |

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| unit == "m" || upper == "MIB" -> return v |

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| unit == "M" || upper == "MB" -> return $ siConvert v |

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| unit == "g" || upper == "GIB" -> return $ v * 1024 |

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| unit == "G" || upper == "GB" -> return $ siConvert |

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(v * 1000) |

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| unit == "t" || upper == "TIB" -> return $ v * 1048576 |

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| unit == "T" || upper == "TB" -> return $ |

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siConvert (v * 1000000) |

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| otherwise -> fail $ "Unknown unit '" ++ unit ++ "'" |

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