Comment author: administrator

One feature that (I think) Module Arg could benefit by is more
descriptive and automated help. I'd like to have a

Arg.Symbol of (string * 'a) list * ('a -> unit)

I have tried to implement this, but it needs modifications. The compiler
complains that the type variable 'a is not bound. If I bind it as an
argument to the "spec" type, then we have two problems:

1. It is an incompatible change.
2. It forces all your Symbol options to use the same 'a type.

So what I have done is:
Arg.Symbol of string list * (string -> unit)

And it is your function that has to turn the string into whatever it
needs. One problem with this solution is that your list of symbols
will appear twice in the program (in your function, and in your spec
list).

Another way of doing things would be to give one function for each
symbol, like this:
Arg.Symbol of (string * (unit -> unit)) list

But I don't much like this solution, as it is really heavyweight.
If you have a better idea, please tell me.

"-foobar", Arg.Symbol (["foo",Foo; "bar",Bar], foobar_handler, "foobar?");
"-sex", Arg.Symbol (["male",Male; "female",Female], sex_handler, "sex");

would print as

-foobar [foo|bar] foobar?
-sex [male|female] sex

Pretty much, but square brackets usually denote optional arguments,
so I have used curly braces.

Implemented in the current working version (3.06+14).

It would also be nice if the message for Arg.String and Arg.Int,
etc. mentions that the options takes an argument of the specified
type. This might make some of the messages a little less descriptive.
For example instead of
-cc Use as the C compiler and linker
it would now say
-cc string Use as the C compiler and linker

I don't like it much, but if you want your program to do it, you
can already do it: just write your documentation strings accordingly.

-- Damien