## root / Ganeti / HTools / Utils.hs @ c6484f0b

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{-| Utility functions -} |
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{- |

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Copyright (C) 2009 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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( |

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debug |

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, sepSplit |

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, fst3 |

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, varianceCoeff |

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, commaJoin |

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, readEitherString |

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, loadJSArray |

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, fromObj |

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, asJSObject |

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, asObjectList |

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, fromJResult |

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) where |

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import Data.List |

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import Control.Monad |

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import qualified Text.JSON as J |

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import Text.Printf (printf) |

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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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-- * Miscelaneous |

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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 string on a separator and return an array. |

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sepSplit :: Char -> String -> [String] |

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sepSplit sep s |

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| x == "" && xs == [] = [] |

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| xs == [] = [x] |

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| 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 version of 'fst' for a triple |

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fst3 :: (a, b, c) -> a |

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fst3 (a, _, _) = a |

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-- * Mathematical functions |

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

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-- | Mean value of a list. |

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meanValue :: Floating a => [a] -> a |

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meanValue lst = (sum lst) / (fromIntegral $ length lst) |

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-- | Squaring function |

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square :: (Num a) => a -> a |

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square = (^ 2) |

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-- | Standard deviation. |

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stdDev :: Floating a => [a] -> a |

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stdDev lst = |

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let mv = meanValue lst |

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av = sum $ map square $ map (\e -> e - mv) lst |

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bv = sqrt (av / (fromIntegral $ length lst)) |

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in bv |

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-- | Coefficient of variation. |

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varianceCoeff :: Floating a => [a] -> a |

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varianceCoeff lst = (stdDev lst) / (fromIntegral $ length lst) |

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-- * JSON-related functions |

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-- | Converts a JSON Result into a monadic value. |

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fromJResult :: Monad m => J.Result a -> m a |

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fromJResult (J.Error x) = fail x |

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fromJResult (J.Ok x) = return x |

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-- | Tries to read a string from a JSON value. |

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-- |

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-- In case the value was not a string, we fail the read (in the |

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-- context of the current monad. |

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readEitherString :: (Monad m) => J.JSValue -> m String |

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readEitherString v = |

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case v of |

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J.JSString s -> return $ J.fromJSString s |

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_ -> fail "Wrong JSON type" |

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-- | Converts a JSON message into an array of JSON objects. |

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loadJSArray :: (Monad m) => String -> m [J.JSObject J.JSValue] |

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loadJSArray s = fromJResult $ J.decodeStrict s |

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-- | Reads a the value of a key in a JSON object. |

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fromObj :: (J.JSON a, Monad m) => String -> J.JSObject J.JSValue -> m a |

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fromObj k o = |

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case lookup k (J.fromJSObject o) of |

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Nothing -> fail $ printf "key '%s' not found in %s" k (show o) |

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Just val -> fromJResult $ J.readJSON val |

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-- | Converts a JSON value into a JSON object. |

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asJSObject :: (Monad m) => J.JSValue -> m (J.JSObject J.JSValue) |

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asJSObject (J.JSObject a) = return a |

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asJSObject _ = fail "not an object" |

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-- | Coneverts a list of JSON values into a list of JSON objects. |

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asObjectList :: (Monad m) => [J.JSValue] -> m [J.JSObject J.JSValue] |

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asObjectList = sequence . map asJSObject |