[wg-camlp4] A new branch to experiment with extension points

[Alain Frisch]

On 03/01/2013 09:08 AM, Mark Shinwell wrote:
> 1. If possible, I'd rather see one new syntactic form, rather than
> three.

I've made the syntax more uniform, dropped prefix attributes, and added 
attributes on type declarations.

The current syntax is:

Attributes:

   On expressions:         expr (:foo expr)
   On type expressions:    type (:foo expr)
   On structure items:     str_item ..(:foo expr)
   On type declarations:   type t = ... with (:foo1 expr1) (:foo2 expr2)

Extension nodes:

   On expressions:         (&foo expr)
   On type expressions:    (&foo expr)
   On structure items:     ..(&foo expr)


A type-conv like example (attributes on type expressions and type 
declarations):


=================================================
  type t = {
     x : int (:default 42);
     y : int (:default 3) (:sexp_drop_default);
     z : int (:default 3) (:sexp_drop_if z_test);
  } with (:sexp)
=================================================


A Bisect-like example (attributes on expressions and structure items):

=================================================
let f x =
   match List.map foo [x; a x; b x] with
   | [y1; y2; y3] -> tata
   | _ -> (assert false) (:bisect visit)


let unused = ()
..(:bisect ignore)
=================================================


A Bolt-like example (extension nodes on expressions):

=================================================
let funct n =
   (&log) "funct(%d)" n LEVEL DEBUG;
   for i = 1 to n do
     print_endline "..."
   done
=================================================

or:

=================================================
let funct n =
   (&log "funct(%d)" n LEVEL DEBUG);
   for i = 1 to n do
     print_endline "..."
   done
=================================================


A map/fold generator (extension nodes on structure item):

=================================================
type variable = string
  and term =
   | Var of variable
   | Lam of variable * term
   | App of term * term


..(&generate_map map term)
=================================================

or, if we also add extension nodes on class expressions:

=================================================
type variable = string
  and term =
   | Var of variable
   | Lam of variable * term
   | App of term * term


class map = (&generate_map term)
=================================================



-- Alain