https://github.com/paurkedal/ppx_compose

Composition Inlining for OCaml
https://github.com/paurkedal/ppx_compose

combinator function-composition ocaml optimization ppx-rewriter

Last synced: 5 days ago
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Composition Inlining for OCaml

• Host: GitHub
• URL: https://github.com/paurkedal/ppx_compose
• Owner: paurkedal
• License: lgpl-3.0
• Created: 2017-03-16T23:03:36.000Z (almost 8 years ago)
• Default Branch: master
• Last Pushed: 2021-10-12T19:41:45.000Z (over 3 years ago)
• Last Synced: 2025-01-10T22:47:36.952Z (15 days ago)
• Topics: combinator, function-composition, ocaml, optimization, ppx-rewriter
• Language: OCaml
• Size: 42 KB
• Stars: 1
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGES.md
  • License: COPYING

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README

        
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## `ppx_compose` - Inlined Function Composition

`ppx_compose` is a simple syntax extension which rewrites code containing

function compositions into composition-free code, effectively inlining the

composition operators.  The following two operators are supported

```ocaml

let (%) g f x = g (f x)

let (%>) f g x = g (f x)

```

Corresponding definitions are not provided, so partial applications of `(%)`

and `(%>)` will be undefined unless you provide the definitions.

The following rewrites are done:

  * A composition occurring to the left of an application is reduced by

    applying each term of the composition from right to left to the

    argument, ignoring associative variations.

  * A composition which is not the left side of an application is first

    turned into one by η-expansion, then the above rule applies.

  * Any partially applied composition operators are passed though unchanged.

E.g.

```ocaml

h % g % f ==> (fun x -> h (f (g x)))

h % (g % f) ==> (fun x -> h (f (g x)))

(g % f) (h % h) ==> g (f (fun x -> h (h x)))

```

### Is It Needed?

Recent flambda-enabled compilers can inline the following alternative

definitions of the composition operators [[1]]:

```ocaml

let (%) g f = (); fun x -> g (f x)

let (%>) f g = (); fun x -> g (f x)

```

so this syntax extension will likely be retired at some point.

[1]: https://discuss.ocaml.org/t/ann-ppx-compose-0-0-3/345