Re: How to use modules in place of Type Classes

I think this part of SML has not enough features. However, is there any 
problem if a user of your library does

structure MyGetopt = Getopt (MyDict)

and uses his own MyGetopt after that?

If that is not possible I agree that there can be threading of functors.

BTW, A very interesting article I red about this problem is

Xavier Leroy: Applicative functors and fully transparent higher-order 
modules

and I also posted a question about this in comp.lang.ml earlier.

  - Vesa

On Wed, 27 Dec 2006, David Eger wrote:

> I'm writing a library to do command line parsing in SML much like
> the C getopt() function.  I take a dictionary of expected arguments
> and their types and a command line string.  I return a dictionary of
> parsed arguments.
>
> I don't really care what sort of dictionary I'm passed.
>
> In order for me to make a generalized GETOPT that accepts any sort of
> dictionary, it seems that I have to write my module as a functor, taking
> a structure argument and that each of my callers has to explicitly
> evaluate the functor.  This means that the implementation information
> about the underlying representation of a particular dictionary needs to
> be threaded through any code base that uses my library all the way down
> to the invocation of getopt().
>
> This seems to add a lot of programmer overhead.  Is there a better way?
> Is there any equivalence to the type class sugar of Haskell that I could use?
>
> In practice, do SML users just accept a very specific dictionary and have
> the caller do the manual conversions?  Do they functorize everything?
>
> -David
>
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