> Applying g to 1 you will definitely have f x of type int and you have to
> take care of the returned integer. Unfortunatly caml emits no warning in
> this case (even if I understand why) :(.
>   
    Sure :) But as far as I understand this warning means "this non-unit 
value will definitely be omitted, and this
can be possibly wrong". Under this interpretation the compiler has to 
ensure undoubtedly that the value is
always non-unit.
    BTW you may (temporarily) change your code into something like

    let f x = [x]

    of even into

    let f x = object method get = x end

    and find all the suspicious places :)

    Best regards,
    Dmitri.