hflags

Command line flag parser, very similar to Google's gflags

The @HFlags@ library supports easy definition of command line flags, reimplementing the ideas from Google's @gflags@ (<http://code.google.com/p/gflags>). Command line flags can be declared in any file at the toplevel, using 'defineFlag'. At runtime, the actual values are assigned to the toplevel @flags_name@ constants. Those can be used purely throughout the program. At the beginning of the @main@ function, @$initHFlags \"program description\"@ has to be called to initialize the flags. All flags will be initialized that are transitively reachable via imports from @main@. This means, that any Haskell package can easily define command line flags with @HFlags@. This feature is demonstrated by <http://github.com/errge/hflags/blob/master/examples/ImportExample.hs> and <http://github.com/errge/hflags/tree/master/examples/package>. A simple example (more in the <http://github.com/errge/hflags/tree/master/examples> directory): @ \#!\/usr\/bin\/env runhaskell &#x7b;-\# LANGUAGE TemplateHaskell \#-&#x7d; import HFlags 'defineFlag' \"name\" \"Indiana Jones\" \"Who to greet.\" 'defineFlag' \"r:repeat\" (3 + 4 :: Int) \"Number of times to repeat the message.\" main = do s <- $initHFlags \"Simple program v0.1\" &#x20; sequence_ $ replicate flags_repeat greet &#x20; putStrLn $ \"Your additional arguments were: \" ++ show s &#x20; putStrLn $ \"Which is the same as: \" ++ show HFlags.arguments &#x20; where &#x20; greet = putStrLn $ \"Hello \" ++ flags_name ++ \", very nice to meet you!\" @ At @initHFlags@ time, the library also tries to gather flags out of environment variables. @HFLAGS_verbose=True@ is equivalent to specify --verbose=True. This environment feature only works with long options and the user has to specify a value even for Bools. /Since version 0.2, you mustn't put the initHFlags in a parentheses with the program description. Just/ @$initHFlags@, /it's cleaner./ See <http://github.com/errge/hflags/tree/master/changelog> for recent changes.

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