Re: [Caml-list] I need a C preprocessor

[Issac Trotts <ijtrotts@ucdavis.edu>]

Richard Jones wrote:

>Here is some code I've just written. CjsConfig.debug_menu is a
>compile-time constant.
>
>  let debug_menu =
>    if CjsConfig.debug_menu then
>      Some (factory#add_submenu "Debug")
>    else
>      None in
>
>  (* ... *)
>
>  let single_step_ev_item, single_step_res_item, step_to_item,
>      dump_hiertext_item =
>    match debug_menu with
>      None -> None, None, None, None
>    | Some debug_menu ->
>	let factory = new GMenu.factory debug_menu ~accel_group in
>	let single_step_ev_item =
>	  factory#add_item "Single Step (1 Event)"
>	    ~key:GdkKeysyms._T in
>	let single_step_res_item =
>	  factory#add_item "Single Step (1 Result Period)"
>	    ~key:GdkKeysyms._Z in
>	let step_to_item = factory#add_item "Step To ..." in
>	factory#add_separator ();
>	let dump_hiertext_item =
>	  factory#add_item "Dump HierText To Console"
>	    ~key:GdkKeysyms._H in
>	(Some single_step_ev_item, Some single_step_res_item,
>	 Some step_to_item, Some dump_hiertext_item)
>  in
>
>Now in C I'd use the preprocessor:
>
>#ifdef DEBUG_MENU
>  factory#add_submenu "Debug"
>#endif
>
>#ifdef DEBUG_MENU
>  let factory = new GMenu.factory debug_menu ~accel_group in
>  let single_step_ev_item = factory#add_item "Single Step (1 Event)"
>  (* etc. *)
>#endif
>
>which results in briefer, faster and simpler to understand code.
>
>My question is what is the proper style for this sort of thing in
>OCaml?
>
>Rich.
>
Here's one way, using the C preprocessor:

(* gargle.ml
   ocamlc pp cpp -o gargle gargle.ml *)
  
#define GARGLE

#ifdef GARGLE
let () = prerr_endline "gargle is defined!"
#else
let () = prerr_endline "gargle is not defined!"
#endif



Here's another way, using the camlp4 ifdef macro:

(* gargle2.ml
   ocamlc -pp "camlp4o pa_o.cmo pa_ifdef.cmo pr_o.cmo" -o gargle2 
gargle2.ml *)

define GARGLE

let () =
  ifdef GARGLE
    then prerr_endline "gargle is defined."
    else prerr_endline "gargle is not defined."


Issac




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