Mr. Env

-- Read environment variables, with defaults
host <- envAsString "HOST" "localhost"
port <- envAsInt "PORT" 8000

Simple Example

import System.Environment.MrEnv ( envAsBool, envAsInt, envAsInteger, envAsString )
main :: IO ()
main = do
 -- Get a string, with a fallback value if nothing is set.
 host <- envAsString "HOST" "localhost"
 -- Get an int. If you need an integer instead you could also use envAsInteger.
 port <- envAsInt "PORT" 8000
 -- Get a boolean. Here we're expecting the environment variable to read
 -- something along the lines of "true", "TRUE", "True", "truE" and so on.
 debug <- envAsBool "DEBUG" False
 putStrLn $
 "Let's connect to "
 ++ host
 ++ " on port "
 ++ show port
 ++ ". Debug mode is "
 ++ if debug then "on" else "off"
 ++ "."

Fancy Example

import System.Environment.MrEnv ( envAsBool, envAsInt, envAsInteger, envAsString )
data Config =
 Config { host :: String
 , port :: Int
 , debug :: Bool
 }
getConfig :: IO Config
getConfig = Config
 <$> envAsString "HOST" "localhost"
 <*> envAsInt "PORT" 8000
 <*> envAsBool "DEBUG" False
main :: IO ()
main =
 getConfig >>= \conf ->
 putStrLn $
 "Let's connect to "
 ++ host conf
 ++ " on port "
 ++ show $ port conf
 ++ ". Debug mode is "
 ++ if debug conf then "on" else "off"
 ++ "."

Authors

License