ref: b4a7a0d4c04ad0fb96d0b279d35da2658d58a0e1
dir: /lib/System/Environment.hs/
-- Copyright 2023 Lennart Augustsson
-- See LICENSE file for full license.
module System.Environment(
getArgs,
getProgName,
withArgs,
lookupEnv,
getEnv,
) where
import Prelude(); import MiniPrelude
import Primitives
import Foreign.C.String
import Foreign.Ptr
import System.IO
-- primArgRef returns an array containing a list of strings.
-- The first element is the program name, the rest are the arguments.
getArgs :: IO [String]
getArgs = do
aa <- primGetArgRef
as <- primArrRead aa 0
return $ tail as -- drop program name
getProgName :: IO String
getProgName = do
aa <- primGetArgRef
as <- primArrRead aa 0
return $ head as -- get program name
withArgs :: forall a . [String] -> IO a -> IO a
withArgs as ioa = do
aa <- primGetArgRef
old <- primArrRead aa 0
primArrWrite aa 0 $ head old : as -- keep program name
a <- ioa
primArrWrite aa 0 old
return a
foreign import ccall "getenv" c_getenv :: CString -> IO CString
lookupEnv :: String -> IO (Maybe String)
lookupEnv var = do
cptr <- withCAString var c_getenv
if cptr == nullPtr then
return Nothing
else
Just <$> peekCAString cptr
getEnv :: String -> IO String
getEnv var = do
mval <- lookupEnv var
case mval of
Nothing -> error $ "getEnv: not found " ++ var
Just val -> return val