ghc-hflags

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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License: Apache-2.0
URL: https://hackage.haskell.org/package/hflags