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Scripting in ocaml
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Date: 2006-12-22 (18:16)
From: skaller <skaller@u...>
Subject: Re: strong/weak typing terminology (was Re: [Caml-list] Scripting in ocaml)
On Fri, 2006-12-22 at 17:51 +0100, Tom wrote:
>         Later he gives the following chart
>                 |Statically checked       | Dynamically checked 
>         -------------------------------------------------
>         safe   | ML, Haskell, Java, etc. | Lisp, Scheme, Perl,
>         Postscript, etc
>         unsafe | C, C++, etc.            |
> But this chart is not expressive enough...

It is also unclear what you mean by 'unsafe'.

Ocaml is not safe:

	let a = Array.create 0 0 in
	let y = a.[99] in (* WOOPS *)

The fact that an exception is thrown may or may not
make the language safe depending on whether or not
you INTEND to trigger an exception. The best you can
say is that if you don't catch it, its a bug.

Otherwise, you have to read the comments to know if
the out of bounds access was deliberate .. something
compilers can't do very easily. 

In fact C arrays are safer precisely because the behaviour
is not defined. That way you KNOW an out of bound access is
an error, so reasoning about the code .. and optimising it ..
is easier.

Furthermore you can always enable array bounds checking
with an instrumentation switch or tool like Purify.

Well array bounds probably aren't contentious: most people
would say an access violation was a bug, even in Ocaml.
But you can't be so sure with

	try Some (Hashtbl.find table key) 
	with Not_found -> None

That doesn't look like a bug, if the key isn't found.

There's a difference in intent .. but the language
fails to express it. Exceptions and specified dynamic
checks are 'evil' :)

John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: