[Haskell] ANNOUNCE multiarg - parser combinators for command line parsing

[Omari Norman]

> I'm currently using Neil Mitchell's cmdargs package [1]. How does your
> package compare to that?

Hi Simon,

If you're using cmdargs and you're happy with it, you should certainly
stick with it, as it certainly has many capabilities that multiarg does
not, as well as being much better tested :)

I examined cmdargs before writing multiarg; the main reason I decided to
write something myself is because cmdargs offers no (apparent) way to
create options that take more than one argument, such as "--pair thing1
thing2". Some programs do have options that really take more than one
logical argument but, as far as I can tell, most of them resort to
tricks such as putting both options in a single word and using
characters such as : or = to delimit them. (mplayer is a good example of
this.) I figure that the shell already does the hard work of splitting
things into words, so the parser should be able to parse options that
accept more than one word as arguments.

multiarg aims to be modular, like a parser combinator library. By taking
a few simple pieces you can build very complex parsers. For instance,
there is no explicit support for multiple-mode commands (e.g. "darcs
whatsnew", "darcs send", etc.) multiarg does not need such support
because there are a couple of parsers (nextArg, nonOptionPosArg) that
can be easily used to parse modes, arguments to options, or positional
arguments.

cmdargs does a lot of things that multiarg will never do--for instance,
it creates help automatically and even creates zsh completions
automatically. This is a nifty feature but I always find these sort of
things frustrating and I would rather just write the help in a text
editor.

For a sample module that uses multiarg, see Pantry:

https://github.com/massysett/Pantry/blob/master/Pantry/Parser.hs

--Omari