Written by John Goerzen, jgoerzen@complete.org

Utilities for command-line parsing, including wrappers around the standard System.Console.GetOpt module.

Simple command line parser -- a basic wrapper around the system's default getOpt. See the System.Console.GetOpt manual for a description of the first two parameters.

The third parameter is a usage information header.

The return value consists of the list of parsed flags and a list of non-option arguments.

Similar to parseCmdLine, but takes an additional function that validates the post-parse command-line arguments. This is useful, for example, in situations where there are two arguments that are mutually-exclusive and only one may legitimately be given at a time.

The return value of the function indicates whether or not it detected an error condition. If it returns Nothing, there is no error. If it returns Just String, there was an error, described by the String.

A type to standardize some common uses of GetOpt.

The first component of the tuple is the long name of the option.

The second component is empty if there is no arg, or has the arg otherwise.