https://github.com/slamko/ppx_catch

Ocaml PPX for no-exception error handling
https://github.com/slamko/ppx_catch

error-handling functional-programming meta-programming no-exception ocaml ppx ppx-extension ppx-rewriter ppxlib

Last synced: 3 months ago
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Ocaml PPX for no-exception error handling

• Host: GitHub
• URL: https://github.com/slamko/ppx_catch
• Owner: slamko
• License: gpl-3.0
• Created: 2023-07-26T19:04:10.000Z (about 2 years ago)
• Default Branch: master
• Last Pushed: 2023-07-27T13:30:44.000Z (about 2 years ago)
• Last Synced: 2025-03-14T21:41:43.760Z (7 months ago)
• Topics: error-handling, functional-programming, meta-programming, no-exception, ocaml, ppx, ppx-extension, ppx-rewriter, ppxlib
• Language: OCaml
• Homepage:
• Size: 17.5 MB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.org
  • License: LICENSE

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README

          
*** Simple PPX rewriter to catch exceptions and wrap the result into ('a, string) result

**** Overview

May be useful to handle the case when the function inside List.map fails:

#+begin_src ocaml

let%catch func lst =

  List.map (fun x ->

    if x > 0 then failwith "Some problem" else x + 1) lst 

#+end_src

becomes:

#+begin_src ocaml

let%catch func lst =

  try

    Ok (List.map (fun x ->

      if x > 0 then failwith "Some problem" else x + 1) lst)

  with

  | Failure err -> Error (*[ "func: " + err ]*) (* error messages with tracing *)

    (* and so on *) ...

  | _ -> Error "func: Unknown error" 

#+end_src

Extension handles both top-level and "embedded" let bindings:

#+begin_src ocaml

let foo =

  let%catch wants_to_raise () = (* wrap some Stdlib function for example *)

    (* some logic *)

    failwith "Stdlib exception" (* call to Stdlib function that raises an exception *)

  in

  wants_to_raise () (* returns ('a, string) result *)

#+end_src

Also works with "function" syntax:

#+begin_src ocaml

let%catch wrap_function = function

  | Some res -> res

  | None -> failwith "function syntax works too"

#+end_src

It basically wraps each case of the pattern matching.

#+begin_src ocaml

let () =

  match wrap_function None with

  | Ok ok -> Printf.printf "Ok\n" ;

  | Error err -> Printf.printf "%s\n" err ;

  () 

#+end_src

prints :

#+begin_src sh

wrap_function: function syntax works too

#+end_src

**** Quickstart

To instal this rewriter as opam package:

#+begin_src sh

git clone https://github.com/slamko/ppx_catch.git &&

cd ppx_catch &&

dune build &&

opam install .

#+end_src

Now to use it in your project add ppx_catch to library list

and tell to use it as a preprocessor in your dune file:

#+begin_src lisp

(libraries

            ppx_catch)

(preprocess (pps ppx_catch))

#+end_src

For a complete dune file example see test/dune

**** LICENSE

GPL-v3.0