https://github.com/Astrocoders/lenses-ppx

GADT lenses
https://github.com/Astrocoders/lenses-ppx

ocaml ppx reasonml

Last synced: 2 months ago
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GADT lenses

• Host: GitHub
• URL: https://github.com/Astrocoders/lenses-ppx
• Owner: Astrocoders
• License: mit
• Created: 2018-12-25T19:53:33.000Z (about 6 years ago)
• Default Branch: master
• Last Pushed: 2021-10-16T17:05:25.000Z (over 3 years ago)
• Last Synced: 2024-08-03T01:29:23.292Z (6 months ago)
• Topics: ocaml, ppx, reasonml
• Language: Reason
• Homepage:
• Size: 227 KB
• Stars: 105
• Watchers: 8
• Forks: 10
• Open Issues: 8
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

• awesome-list - lenses-ppx

README

        
# What are GADTs?

[GADTs: A primer](https://sketch.sh/s/yH0MJiujNSiofDWOU85loX/)

# Why

Differently from normal lenses/optics the following approach allows for composing "lenses" into lists/arrays which is them useful for things like https://github.com/rescriptbr/reschema

# Install

Install the last stable version

For ReScript

```

npm install --save-dev lenses-ppx@latest

or

yarn add lenses-ppx@latest -D

```

For BuckleScript < 6

```

npm install --save-dev [email protected]

or

yarn add [email protected] -D

```

# Build

```

npm run build

```

# Watch

```

npm run watch

```

In

```rescript

module StateLenses = %lenses(

  type state = {

    email: string,

    age: int,

  }

)

```

Out

```rescript

module StateLenses = {

  type state = {

    email: string,

    age: int,

  }

  type rec field<_> =

    | Email: field

    | Age: field

  let get:

    type value. (state, field) => value =

    (state, field) =>

      switch field {

      | Email => state.email

      | Age => state.age

      }

  let set:

    type value. (state, field, value) => state =

    (state, field, value) =>

      switch field {

      | Email => {...state, email: value}

      | Age => {...state, age: value}

      }

}

```

Using

```rescript

open StateLenses

let state = {email: "[email protected]", age: 969}

Js.log(state->get(Email))

Js.log(state->get(Age))

```

Alternatively you can also use it like

```rescript

@lenses @decco

type bartux = {

  color: string,

  top: int,

}

let bartux = {color: "red", top: 10}

Js.log(bartux->bartux_get(Color))

Js.log(bartux->bartux_set(Top, 20))

Js.log(bartux_encode(bartux))

```

Alternatives

- https://github.com/scoville/re-optic/blob/master/docs/lenses-ppx.md which is more strict and follows more closely Optics standards