Re: [Caml-list] Pattern matching on refs

[Yotam Barnoy <yotambarnoy@gmail.com>]

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It wouldn't solve the problem, because in reality I'm matching something
like this piece of code implementing a doubly-linked list:

type 'a cell = { data : 'a;
                 next : 'a link ref;
                 last : 'a link ref;
               }

and 'a link = Cons of 'a cell | Nil

type 'a t = {
  firstl: 'a link ref;
  lastl:  'a link ref;
}

  let pop s = match s with
    | {firstl = {contents=Nil}; lastl = _ } -> raise Empty

    | {lastl = {contents=Cons {data; _}}} when s.lastl == s.firstl ->
        (* one term *)
        s.lastl := Nil;
        s.firstl := Nil;
        data

    | {firstl =
      {contents=Cons {data; next={contents=Cons n}; last={contents=Nil}}}}
->
        n.last := Nil;
        s.firstl := Cons n;
        data
    | _ -> failwith "Error in pop"


See how unwieldy that is without the ability to clean it up by matching on
refs?

-Yotam


On Thu, Oct 10, 2013 at 3:34 PM, Ashish Agarwal <agarwal1975@gmail.com>wrote:

> Would it solve your problem to instead write:
>
> match !x with
> | y -> ...
>
>
> On Thu, Oct 10, 2013 at 3:17 PM, Yotam Barnoy <yotambarnoy@gmail.com>wrote:
>
>> I recently found out how ugly it is to pattern-match on a ref, using
>> {contents=...}. This should be extremely easy to fix in the parser. Can it
>> please be put into the next version of ocaml?
>> ie.
>>
>> match x with
>> | ref y -> ...
>>
>> -Yotam
>>
>
>

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