I've read the May interchange in CWN that started with the question

> I have made a web search to understand which kind of support for 
> bignums is available for OCaml...

and found it interesting. I'll be teaching a few weeks of ML as part 
of a first-year course at Brown University, and we've used SML in 
previous years. SML/NJ works OK, but we'd like a debugger, so I've 
looked at OCaml as a possible alternative. I was a little depressed 
to find (by trial and error) that "int" doesn't mean "integer" but 
rather "element of Z/nZ for some very large n, represented with 
integer notation, including negative signs." 

I think I can live with this if only there's some way to write 
something like this (pseudo-ML/Java):

fun fact(0) = 1
  | fact(n) = try {
                 n * fact(n-1)
              }
              catch (IntegerOverflow e) ...


What I don't think I can bear is to use the sorts of "bignum"-like 
libraries that make me write things like

 y = x bigadd big-unit

to mean 

 y = x + 1

because our students will actually be writing some code that has 
a good deal of arithmetic in it. 

---

So the questions are

1. Is there a way to catch overflow exceptions within an entire 
   computation?
2. Is there a way to tell OCaml that ints really are either 
   (a) bignums or
   (b) overflow-protected ints (as in SML/NJ, for instance)

Perhaps the implicit third question is

3. Is there a reasonable debugger for some dialect of ML that has 
what I might call "protected integers"? 

Thanks very much in advance. 

-John Hughes

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