Re: [Caml-list] Pattern matching of records

[Gerd Stolpmann <info@gerd-stolpmann.de>]

[-- Attachment #1: Type: text/plain, Size: 1823 bytes --]

Am Mittwoch, den 16.09.2015, 14:19 +0200 schrieb Leonardo Laguna Ruiz:
> I have the following type
> 
> (* File: S.ml *)
> module S = struct
>     type s =
>        {
>           a : int;
>           b : int;
>        }
> end
> 
> 
> I I have found that for creating records I can do as follows:
> 
> (* File: main.ml *)
> open S
> let s0 = S.{ a = 0; b = 0}
> 
> 
> However this does not work for pattern matching:
> 
> (* this does not work *)
> match s0 with
> | S.{ a = 0 ; b = 0 } -> true
> | _ -> false

You are thinking the right way, but you run into a well-known
shortcoming: http://caml.inria.fr/mantis/view.php?id=6656

Gerd

> 
> 
> These two alternatives work, but one with a warning and the other 
> (depending on the type) is too verbose:
> 
> (* this produces a warning *)
> match s0 with
> | { a = 0 ; b = 0 } -> true
> | _ -> false
> 
> (* this works *)
> match s0 with
> | { S.a = 0 ; S.b = 0 } -> true
> | _ -> false
> 
> 
> Is there any other way of writing pattern matches as compact as S.{ a = 
> 0 ; b = 0 } ? (which is consistent to the construction of the same value)
> 
> I know that it's possible to do:
> 
> let open S in
> match s0 with
> | { a = 0 ; b = 0 } -> true
> | _ -> false
> 
> but the main reason I don't do it is because I have more records like:
> 
> match s0,k0 with
> | { S.a = 0 }, {K.a = 0 } -> true
> 
> 
> 
> Best regards,
> 
> Leonardo
> 
> 
> 

-- 
------------------------------------------------------------
Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
My OCaml site:          http://www.camlcity.org
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
------------------------------------------------------------

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 473 bytes --]