hsoptions

Haskell library that supports command-line flag processing.

Too see an user guide and list of features go to https://github.com/josercruz01/hsoptions#table-of-contents.

Flags are declared in the code by using the make function, which takes the flag's name, help text and type as arguments.

The flags are parsed from the command line stream of from a file if the --usingFile <filename> flag is sent to the program.

Flags can be customized by calling configuration function, such as defaultIs or aliasIs, that change how the flag behaves, how it is parsed and validated.

The processMain function needs to be called at the beginning of the main function. This function takes as arguments:

• The program description

• A list of all declared flags

• Three callbacks:

• * success

• * failure

• * display help

If there is any kind of validation error failure is called with the list of errors. If the --help flag was sent by the user display help is called. Otherwise if there are no problems the success function is called.

A default implementation of failure and display help is provided in the library (defaultDisplayHelp, defaultDisplayErrors) with a basic bahavior.

Basically success becomes the 'real' main function. It takes as argument a tuple (FlagResults, ArgsResults). FlagResults is a data structure that can be used to query flags by using the get function. ArgsResults is just an array of String containing the remaining not-flag arguments.

A simple example (more in https://github.com/josercruz01/hsoptions/tree/master/examples)

import System.Console.HsOptions

userName = make ( "user_name",
                , "the user name of the app",
                , [ parser stringParser,
                  , aliasIs ["u"]
                  ]
                )
userAge = make ("age", "the age of the user", [parser intParser])

flagData = combine [flagToData userName, flagToData userAge]

main :: IO ()
main = processMain "Simple example for HsOptions."
                   flagData
                   success
                   failure
                   defaultDisplayHelp

success :: ProcessResults -> IO ()
success (flags, args) = do let nextAge = (flags `get` userAge) + 5
                           putStrLn ("Hello " ++ flags `get` userName)
                           putStrLn ("In 5 years you will be " ++
                                     show nextAge ++
                                     " years old!")

failure :: [FlagError] -> IO ()
failure errs = do putStrLn "Some errors occurred:"
                  mapM_ print errs

At the processMain function each of the input flags is validated against the declared flags. Within the success function you can be sure that all required flags exist, all flag types are correct and all validation was successful.