a short cut syntax for functional FFI

[bobzhang]

[%%bs.ffi                                                                                                                                                                                                        
type 'a u  =                                                                                                                                                                                                     
  <                                                                                                                                                                                                              
         concat : 'self -> 'self ;                                                                                                                                                                                
         append : 'a  -> 'self  [@bs.send "concat"];                                                                                                                                                                                                                                                                                                                                 
  > as 'self                                                                                                                                                                                                                                                                                                                                                                                                                     
]      

which is equivalent to

type 'a u 
external concat : 'a u -> 'a u -> 'a u = "concat" [@@bs.send]
external append : 'a u -> 'a -> 'a u = "concat" [@@bs.send]

[bobzhang]

in the future, we can derive both functional ffi and class type ffi by the same syntax? @abhirmathur , any comments?

[abhirmathur]

Maybe we can also generate a method create to set any [@@bs.set] properties and create the object.

I found that a common pattern when creating a FFI was:

type table

  (* width *)
  external set_width :  table -> int -> unit = "width" [@@bs.set]
  external get_width : table -> int = "width" [@@bs.get]

  (* height *)
  external set_height : table -> int -> unit = "height" [@@bs.set]
  external get_height : table -> int = "height" [@@bs.get]

  (* new Table *)
  external create_table : unit ->  table = "Table" [@@bs.new]

After this, I would define a set and create method but only expose the create method in the FFI.

(* setter *)
let set table ?width ?height () =
  begin match width with
    | None -> ()
    | Some width -> set_width table width
  end;
  begin match height with
    | None -> ()
    | Some height -> set_height table height
  end;

(* create and set *)
let create ?width ?height () = 
  let table = create_table() in 
  set table ?width ?height  ();
  table

I'm not sure if we can consistently generate the [@@bs.new] constructor correctly.

[bobzhang]

another good thing to do

[%bs.ffi
type 'a u = <
  addEventLisener : [ `Load | `Unload ] -> ('self -> unit [@bs.this]) -> unit 
  (* since we already use ppx, we can do a little further to convert poly-var into string
     provide a better safe FFI
*) 
> as 'self
]

[bobzhang]

this is not the core part of the FFI language, syntactic sugar is nice , we can wait for a while

[github-actions]

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