Re: [Caml-list] let () =

[Richard Jones <rich@annexia.org>]

On Tue, Aug 03, 2004 at 06:46:12PM +0400, Paul Argentoff wrote:
> 
> Hello World!
> 
> Can anyone answer my silly question: what does "let () = bla" really mean?

It means "evaluate 'bla' now".  In this instance, 'bla' is assumed to
be something which evaluates to / returns '()' (ie. the unit value).

There is another related syntax:

let _ = bla

which evaluates 'bla', and ignores the return type of 'bla', whatever
it might be.

Basically, these constructs are a way to evaluate something at
initialization time - usually when the program starts up, or the
module is loaded by some other means such as Dynlink.

These two syntaxes are equivalent:

let _ =
  f1 ();
  f2 ();
  f3 ()

and:

f1 ();;
f2 ();;
f3 ();;

The first is used by people who don't like the ';;' syntax.

I've CC'd this message to ocaml-beginners
[http://groups.yahoo.com/group/ocaml_beginners/] which is a more
appropriate place to discuss this stuff.

Rich.

-- 
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