Synnefo » snf-ganeti

{-| Utility functions -}

module Utils where

import Data.List

import Data.Either

import System

import System.IO

import Monad

import Debug.Trace

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

debug :: Show a => a -> a

debug x = trace (show x) x

-- | Check if the given argument is Left something

isLeft :: Either a b -> Bool

isLeft val =

    case val of

      Left _ -> True

      _ -> False

fromLeft :: Either a b -> a

fromLeft = either (\x -> x) (\_ -> undefined)

fromRight :: Either a b -> b

fromRight = either (\_ -> undefined) id

-- | Comma-join a string list.

commaJoin :: [String] -> String

commaJoin = intercalate ","

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

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

sepSplit sep s

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

    | xs == []            = [x]

    | ys == []            = x:"":[]

    | otherwise           = x:(sepSplit sep ys)

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

          ys = drop 1 xs

-- | Partial application of sepSplit to @'.'@

commaSplit :: String -> [String]

commaSplit = sepSplit ','

-- | Swap a list of @(a, b)@ into @(b, a)@

swapPairs :: [(a, b)] -> [(b, a)]

swapPairs = map (\ (a, b) -> (b, a))

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

-- | Mean value of a list.

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

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

-- | Standard deviation.

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

stdDev lst =

    let mv = meanValue lst

        square = (^ (2::Int)) -- silences "defaulting the constraint..."

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

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

    in bv

-- | Coefficient of variation.

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

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

-- | Get a Right result or print the error and exit

readData :: (String -> IO (Either String String)) -> String -> IO String

readData fn host = do

  nd <- fn host

  when (isLeft nd) $

       do

         putStrLn $ fromLeft nd

         exitWith $ ExitFailure 1

  return $ fromRight nd