infix operator for the revised syntax

infix operator for the revised syntax

[Arturo Borquez]

Dear Camlers,

I've failed do do a syntax extention to the
revised syntax in order to get a *real* infix operator
for function concatenation in order to avoid
excessive parenthesis.

example with lists (silly)

let ( $ ) f g = g (f);; (* provided by normal syntax works fine *)

let r = List.map ... a_list $ List.sort ... $ List.fold_left ... in ..
(* that's i whant to write with the revised syntax *)

let r = List_fold_left ... ((List.sort ...) List.map ... a_list) in ..

thanks in advance
-- 
Arturo Borquez


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Re: [Caml-list] infix operator for the revised syntax

[Michel Mauny]

Hello,

Arturo Borquez wrote/écrivait (Tue, Nov 30, 2004 at 01:50:55PM -0500):
> Dear Camlers,
> 
> I've failed do do a syntax extention to the
> revised syntax
> [...]
> let ( $ ) f g = g (f);; (* provided by normal syntax works fine *)

Please note that using `$' as an operator is explicitely discouraged
in the OCaml manual: http://caml.inria.fr/ocaml/htmlman/manual009.html

Furthermore, there is a bug in Camlp4 3.08.2 that prevents using `$'
as anything else than the antiquotation delimiter in the
Camlp4-preprocessed syntaxes. This is fixed in the CVS (see
http://caml.inria.fr/bin/caml-bugs/fixed?id=3310 foran explanation and
a patch).

> [...] in order to get a *real* infix operator for function
> concatenation in order to avoid excessive parenthesis.

> example with lists (silly)
> 
> let ( $ ) f g = g (f);; (* provided by normal syntax works fine *)

> let r = List.map ... a_list $ List.sort ... $ List.fold_left ... in ..
> (* that's i whant to write with the revised syntax *)
> 
> let r = List_fold_left ... ((List.sort ...) List.map ... a_list) in ..

As far as I understand, what you want is to extend the revised syntax
with a new construct/operator. The Camlp4 documentation is your friend
here (http://caml.inria.fr/camlp4/manual/manual006.html#toc16,
http://caml.inria.fr/camlp4/tutorial/tutorial007.html#toc49, etc.).

For instance (using the revised syntax), the following could help
you. (Change  AFTER ":=" with the precedence level you want.)

  open Pcaml;

  (* Reversed application *)

  value send_to x f = f x;

  EXTEND
    expr: AFTER ":="
      [[ e1 = expr; "sentto"; e2 = expr -> <:expr< send_to $e1$ $e2$ >> ]];
  END;

Hope this helps,

-- Michel Mauny