https://github.com/sim642/ppx_viewpattern

View patterns in OCaml
https://github.com/sim642/ppx_viewpattern

ocaml ppx ppx-rewriter ppxlib

Last synced: 3 months ago
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View patterns in OCaml

• Host: GitHub
• URL: https://github.com/sim642/ppx_viewpattern
• Owner: sim642
• License: mit
• Created: 2022-02-27T21:24:40.000Z (over 3 years ago)
• Default Branch: master
• Last Pushed: 2025-03-15T10:31:51.000Z (4 months ago)
• Last Synced: 2025-03-15T11:19:59.345Z (4 months ago)
• Topics: ocaml, ppx, ppx-rewriter, ppxlib
• Language: OCaml
• Homepage:
• Size: 52.7 KB
• Stars: 11
• Watchers: 3
• Forks: 1
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE.md

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README

        
# ppx_viewpattern

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Transformation for view patterns in OCaml.

_Attempts to_ imitate [Haskell view patterns](https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/view_patterns.html).

## Installation

```console

opam install ppx_viewpattern

```

## Usage

In dune:

```

(preprocess (pps ppx_viewpattern))

```

## Syntax

Use `[%view? pat when exp]` as a pattern to apply `exp` to whatever the pattern is matching and match the result of the `exp` application against `pat`.

Analogous to the Haskell view pattern `exp -> pat`.

See [`example/`](example/) for example usage.

Supported in:

* `match ... with ...` cases,

* `function ...` cases,

* `fun ... -> ...` arguments,

* `let ... in ...` expression binding left-hand sides,

* `try ... with ...` cases,

* nested inside the `pat` and `exp` parts of a view pattern itself.

### Caveats

A view pattern disables `redundant-case` and `partial-match` warnings for the corresponding `match`/`function`.

Currently unsupported in:

- `let ...` definition left-hand sides (at top level or in modules).