Re: [Caml-list] Frustrated Beginner

[Shawn Wagner <shawnw@speakeasy.org>]

On Tue, Dec 23, 2003 at 01:11:08AM -0500, Tyler Eaves wrote:
> 
> On Dec 23, 2003, at 12:34 AM, Matt Gushee wrote:
> >
> >      match foo with
> >      | None -> print_endline "Nothing"; ""
> >      | Some x -> print_endline x; x
> 
> If I understand the match syntax correctly, in this case, x takes the 
> value of foo?

Not quite. foo is an option type - it can hold either Some valid bit of data
(A string in this case), or nothing (None). x ends up taking the value of
whatever the valid bit of data is. The same thing in C would look like

if (foo) {
   puts(foo);
   return foo;
} else {
   puts("Nothing");
   return "";
}

Options are nicer, however, because you don't have the problem that crops up
in C of not handling cases where NULL is a valid bit of data because it's
treated as 'No data'. Hash lookup functions that return NULL when a key's
not found are a classic example. What happens when you want to store NULL in
one?

-- 
Shawn Wagner
shawnw@speakeasy.org

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