[nem-en] Nemerle meets Linq

[Michal Moskal]

On 1/29/06, Alejandro Serrano <trupill at yahoo.es> wrote:
> I've created some type of F#-like Linq integration in Nemerle as a set
> of macros, using the same |> extension.
> However, I need some help with macros, firstly with orderby clauses,
> where I don't know where to start, because
>
> orderby (_.Country), (_.Telephone) descending
>
> must be converted into
>
> |> System.Query.Sequence.ThenByDescending (_, _.Telephone)
> |> System.Query.Sequence.OrderBy (_, _.Country)

Maybe it could be:

  orderby [(_.Country), (_.Telephone)] descending

?

This should parse, and be possible to be eaten by a macro:

  syntax("orderby", expr, Optional("descending"))

or something like that. Maybe even:

  syntax("orderby", expr, Optional(desc))

and check if desc is <[ descending ]>, <[ ascending ]> or whatever.

I don't know if this is what you meant.

>
> Secondly, I don't know how to make:
>
> def n = ["12/03/2004", "1/08/1998"];
> def r = n
>   |> orderby (fun (x) { x })
>   |> select (System.DateTime.Parse(_));
>
> to be parsed as:
>
> def n = ["12/03/2004", "1/08/1998"];
> def r = ( n
>   |> orderby (fun (x) { x }) )
>   |> select (System.DateTime.Parse(_));
>
> instead of:
>
> def n = ["12/03/2004", "1/08/1998"];
> def r = n
>   |> ( orderby (fun (x) { x })
>   |> select (System.DateTime.Parse(_)) );

OK, this one is simple:

[assembly: Nemerle.Internal.OperatorAttribute ("Nemerle.Linq",
  "|>", false, 170, 171)]

Just set a priority, you think makes sense, look at macros/core.n for
examples.

Though I think operators should be left-associative by default. Kamil?

> Finally I would like to know if there is a better way to say this:
>
> def r = n |> orderby (fun (x) {x} );
>
> to order something by itself, because _ alone gives error.

We once had an idea to include Nemerle.Core.identity or something like
that. 'x => x' once we have this syntax also won't be bad.

> I attah by implementation plus a free Linq implementation.

Great! I'll have a look.


--
   Michal Moskal,
   http://nemerle.org/~malekith/