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From: Robert A Duff <bobduff@world.std.com>
Subject: Re: Static typing (Was Re: Better support for garbage collection)
Sender: bobduff@world.std.com (Robert A Duff)
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Date: Sat, 17 Mar 2001 23:45:01 GMT
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Date: 2001-03-17T23:45:01+00:00
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Brian Rogoff <bpr@shell5.ba.best.com> writes:

> # let rec len l = match l with [] -> 0 | x::xs -> 1 + len xs;;
> 
> Hey, where are the types? Is this like Lisp? No, not really, here is what 
> the top level says when I enter that
> 
> val len : 'a list -> int = <fun>
> 
> So the system *infers* the type, and a very general type, for that
> function. It takes a list of anything to an integer. I didn't even need 
> to instantiate a generic for that. Pretty spiffy, huh?

No.  I don't find it spiffy to have to read down into the guts of that
function to find out that it returns an 'int'.  Nor do I find it spiffy
that the type of a literal is determined by what it looks like.  I think
the type of a literal should be determined from context.

I think type inference is spiffy within (small) expressions, but I think
interfaces should have explicitly declared types, including functions
like the above 'len'.

I understand that in ML you *can* declare signatures, *if you like*.
I don't know OCaml, unfortunately.

- Bob