https://github.com/hcarty/ppx_defer

OCaml extension for a Go-ish [%defer ...] syntax
https://github.com/hcarty/ppx_defer

ocaml ocaml-extension ppx

Last synced: about 2 months ago
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OCaml extension for a Go-ish [%defer ...] syntax

• Host: GitHub
• URL: https://github.com/hcarty/ppx_defer
• Owner: hcarty
• License: mit
• Created: 2016-02-10T16:08:51.000Z (almost 9 years ago)
• Default Branch: main
• Last Pushed: 2022-05-30T16:50:54.000Z (over 2 years ago)
• Last Synced: 2023-03-12T05:03:10.297Z (almost 2 years ago)
• Topics: ocaml, ocaml-extension, ppx
• Language: OCaml
• Size: 35.2 KB
• Stars: 17
• Watchers: 2
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGES.md
  • License: LICENSE.md

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README

        
# ppx_defer - Go-like `[%defer later]; now` syntax.

![Build status](https://github.com/hcarty/ppx_defer/workflows/Build%20and%20test%20ppx_defer/badge.svg)

This is an OCaml language extension implementing a somewhat Go-ish

`[%defer expr1]; expr2` which will defer the evaluation of `expr1` until after

`expr2`.  `expr1` will still be evaluated if `expr2` raises an exception.

If you are using Lwt you can use `[%defer.lwt expr1]; expr2`.

Thanks to Drup for guidance in figuring out ppx details!

## Using ppx_defer

As a simple example this code

```ocaml

let () =

  [%defer print_endline "world"];

  print_endline "Hello"

```

will print

```

Hello

world

```

as `print_endline "world"` was deferred until after `print_endline "Hello"`.

A more common use case would be closing an external resource at the end of the

current expression.

```ocaml

let () =

  let ic = open_in_bin "some_file" in

  [%defer close_in ic];

  let length = in_channel_length ic in

  let bytes = really_input_string ic length in

  print_endline bytes

```

This will `close_in ic` at the end of the current expression, even if an

exception is raised.

See the `examples/` directory for more examples.