Re: [Caml-list] what does let () = ... define?

[Nicolas Barnier <barnier@recherche.enac.fr>]

Le 18/03/2016 19:52, Christoph Höger a écrit :
> It defines a match-expression with a single case, that is why you get
> the warning on None. [...]
> The same holds
> for records, tuples etc. think of it as a shallow and cheap type annotation.

Indeed. And it is quite a common idiom to write the equivalent of a "main"
function at the end of a source file as the last called function of your
program shouldn't return any useful value, for example :

let () =
   let x = int_of_string Sys.argv.(1) in
   solve x

It's better practice than to write :

let _ =
   ...

because it can catch some type error that would silently pass with
the latter: suppose you finally decide to add a parameter to the
solve function (let solve = fun x y -> ...), if you forget to add
the argument to the call to solve in the main function, in the first
case you get a type error, but your program compiles and just does
nothing in the second case (_ matches with a partial application of
solve).

Regards,

-- Nicolas