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------------------------------------------------------------------------------
-- | Library to access parts of the system environment.
--
-- Author: Michael Hanus, Bernd Brassel, Bjoern Peemoeller
-- Version: November 2020
------------------------------------------------------------------------------

module System.Environment
  ( getArgs, getEnv, setEnv, unsetEnv, getProgName
  , getHostname, isPosix, isWindows
  ) where

-- | Returns the list of the program's command line arguments.
--   The program name is not included.
getArgs :: IO [String]
getArgs external

-- | Returns the value of an environment variable.
--   The empty string is returned for undefined environment variables.
getEnv :: String -> IO String
getEnv evar = prim_getEnviron $## evar

prim_getEnviron :: String -> IO String
prim_getEnviron external

-- | Set an environment variable to a value.
--   The new value will be passed to subsequent shell commands
--   and visible to subsequent calls to 'getEnv'
--   (but it is not visible in the environment
--   of the process that started the program execution).
setEnv :: String -> String -> IO ()
setEnv evar val = (prim_setEnviron $## evar) $## val

prim_setEnviron :: String -> String -> IO ()
prim_setEnviron external

-- | Removes an environment variable that has been set by 'setEnv'.
unsetEnv :: String -> IO ()
unsetEnv evar = prim_unsetEnviron $## evar

prim_unsetEnviron :: String -> IO ()
prim_unsetEnviron external

-- | Returns the hostname of the machine running this process.
getHostname :: IO String
getHostname external

-- | Returns the name of the current program, i.e., the name of the
--   main module currently executed.
getProgName :: IO String
getProgName external

-- | Is the underlying operating system a POSIX system (unix, MacOS)?
isPosix :: Bool
isPosix = not isWindows

-- | Is the underlying operating system a Windows system?
isWindows :: Bool
isWindows external