optional arguments ?

As part of my x3d interface I'm stuck with the task of filling in  
lots and lots of records, many of which have little used fields which  
can simply be stuffed with a reasonable default.

I would like to create convenient constructor functions which assign  
reasonable defaults to the unassigned fields.

What's a good method to do this in SML ?  Python (and OCAML) allow  
labelled arguments with a default assigned to unspecified args.  I  
don't believe something like this is avaiable for SML.

As of right now the most practical method I can think of is to simply  
pass in an a-list to the constructor.  However even that would be  
somewhat painful since I would have to create an algebraic type for  
the second arg, e.g.

datatype arg = Float of real | Int of int | String of string |  
VectorF of float vector | etc...

So then I could use string * arg for the a-list.

Seems somewhat clumsy.

any way to do this with some clever record notation trick ?


Thanks

Brian


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