はじめてのHaskellプログラム

Ubuntuでバッテリー容量の残量をパーセント表示するプログラムを書いた。

import System.IO

import Text.Regex.Posix

 

getNumber :: String -> Double

getNumber str = read (str =~ "[0-9]+" :: String) :: Double

 

getCapacitance :: String -> String -> Double

getCapacitance ptn lns = getNumber . head . filter (=~ ptn) $ lines lns

 

main = do

  state <- readFile "/proc/acpi/battery/BAT0/state"

  let current = getCapacitance "remaining capacity:" state

  info <- readFile "/proc/acpi/battery/BAT0/info"

  let full = getCapacitance "design capacity:" info

  putStr $ show (floor $ current / full * 100) ++ "%\n"