What are GADTs?
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
module StateLenses = %lenses(
type state = {
email: string,
age: int,
}
)Out
module StateLenses = {
type state = {
email: string,
age: int,
}
type rec field<_> =
| Email: field<string>
| Age: field<int>
let get:
type value. (state, field<value>) => value =
(state, field) =>
switch field {
| Email => state.email
| Age => state.age
}
let set:
type value. (state, field<value>, value) => state =
(state, field, value) =>
switch field {
| Email => {...state, email: value}
| Age => {...state, age: value}
}
}Using
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
@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