Re: [Caml-list] Record field update using 'with' syntax

[Martin Jambon <martin1977@laposte.net>]

On Mon, 18 Sep 2006, Denis Bueno wrote:

> Suppose a module M1 with the record
>
>     type foo = {x : int; y : int; z : int};;
>
> and a member of its type. In another module, a qualified field
> matching like the following works:
>
>     match instance with
>       {M1.x = 5; y = 5; z = 100} -> (* something *)
>
> Why doesn't the following work in a function?
>
>     {M1.instance with x = 20}
       ^^^^^^^^^^^
       this is an arbitrary expression, it doesn't have to come from the
       module where the record type is defined, so you need to specify it
       too.

> Example:

> | # {M1.foo with x = 5};;
> | Characters 0-19:
> |   {M1.foo with x = 5};;
> |   ^^^^^^^^^^^^^^^^^^^
> | Unbound record field label x

That works:

# {M1.foo with M1.x = 0; y = 0};;
- : M1.foo = {M1.x = 0; M1.y = 0; M1.z = 10}


Martin

--
Martin Jambon, PhD
http://martin.jambon.free.fr