rescript-solidjs

Note

This library is in experimental state. A lot of stuff is untested and some of the bindings may simply not work. Feedback is always welcome. Previous versions used HyperScript to make solidJs work with ReScript. This is no longer recommended.

rescript-solidjs allows the use of solidJs with ReScript while still using JSX.

This library consists of two parts

1. It provides bindings for most of the solidJs feature set (see list of missing stuff below). The bindings are as close as possible to the original solidJs naming. In some cases a direct translation wasn't possible. Any deviations are listed in the documentation below.
2. It provides the necessary types to use ReScript without rescript-react. Also some types vary slightly between rescript-react and solidJs, which makes it impossible to use them together.

Also ReScript does not support solidJs natively. A workaround has to be used in order to make them work together. See details below.

Background

Normally, ReScript compiles JSX directly to JavaScript. Therefore it is incompatible with solidJs since it expects the JSX to still be intact and uses their own compiler. Until this is changed (github issue to preserve JSX is already open: https://github.com/rescript-lang/syntax/issues/539) a workaround is required.

Currently there are two solutions that work with this library

1. Use a babel transform to convert compiled ReScript code back to JSX (recommended)
2. Trick the ReScript compiler to actually load HyperScript code instead of the original react code with a fake react implementation

Babel preset

This is the currently recommended way to use this library.

The idea is to use babel to transform compiled ReScript code back to JSX. This is done by a preset that runs multiple transforms to make the code generated by ReScript compatible with solidJs before running it through the solidJs compiler. The corresponding preset can be found here: https://github.com/Fattafatta/babel-preset-rescript-solidjs

Fake react with HyperScript (not recommended)

solidJs supports its own version of HyperScript which could be used together with ReScript and some additional bindings. But using HyperScript instead of JSX is not a great developer experience.

Normally it would be necessary to develop a ppx to modify the behavior of the ReScript compiler, but instead this library uses its own fake version of rescript-react bindings to create the necessary bridge between the code generated by ReScript and the HyperScript expected from solidJs.

Basically the React.createElement function provided by the fake react is replaced by the h function from HyperScript. Most of the magic happens in the src/react/hyper.js file. The rest of the library consists of all the react types required by the ReScript compiler, and the actual solidJs bindings.

Comparison of both approaches

Installation

This library supports the new ReScript versions >= 10.1, but it is backwards-compatible with older versions. For ReScript 10.1 or higher, just install the library normally.

For older versions (< 10.1) additional bsc-flags have to be set (see below).

Library

Install with npm:

npm install solid-js @fattafatta/rescript-solidjs

Or install with yarn:

yarn add solid-js @fattafatta/rescript-solidjs

Add @fattafatta/rescript-solidjs as a dependency to your bsconfig.json:

"bs-dependencies": ["@fattafatta/rescript-solidjs"]

For ReScript < 10.1

Some additional compiler flags have to be set for older versions:

"reason": { "react-jsx": 3 },
"bsc-flags": ["-open ReactV3", "-open SolidV3"],
"bs-dependencies": ["@fattafatta/rescript-solidjs"]

(See also: The migration guide from ReScript)

Babel preset

Using babel to transform ReScript output to SolidJS compatible code. To install the previous version with HyperScript, check the end of this README.

Install with npm:

npm install @fattafatta/babel-preset-rescript-solidjs --save-dev

Or install with yarn:

yarn add @fattafatta/babel-preset-rescript-solidjs --dev

Follow the instructions in the README to configure babel.

Usage

The namings of the bindings are as close as possible to the original solidJs names. In some cases some deviations were necessary to better fit the ReScript type system.

Quick example

A simple counter component. (Note: Building a counter component is actually very tricky in react. But in solidJs it's really straightforward and behaves exactly as expected.)

@react.component
let make = () => {
  let (count, setCount) = Solid.createSignal(1, ())

  let timer = Js.Global.setInterval(() => {
    setCount(c => c + 1)
  }, 1000)

  Solid.onCleanup(() => Js.Global.clearInterval(timer))

  <div>
    {`Hello ReScripters! Counter: ${Js.Int.toString(count())}`->React.string}
    <button
      onClick={_ => {
        setCount(c => c - 3)
      }}>
      {"Decrease"->React.string}
    </button>
  </div>
}

Reactivity

createSignal

The original ~options argument is polymorphic. Use either the #bool or the #fn polymorphic variant to set them.

// normal
let (count, setCount) = Solid.createSignal(1, ())

// with equality options
let (count, setCount) = Solid.createSignal(1, ~options=#bool({equals: false}), ())
// or with equality fn
let (count, setCount) = Solid.createSignal(1, ~options=#fn({equals: (prev, next) => prev == next}), ())

createEffect

let (a, setA) = Solid.createSignal("initialValue", ());

// effect that depends on signal `a`
Solid.createEffect(() => Js.log(a()), ())

// effect with optional initial value
Solid.createEffect(prev => {
  Js.log(prev)
  prev + 1
}, ~value=1, ())

createMemo

Supports the same ~options as createSignal. createMemo passes the result of the previous execution as a parameter. When the previous value is not required use createMemoUnit instead.

let value = Solid.createMemo((prev) => computeValue(a(), prev), ());

// set an initial value
let value = Solid.createMemo((prev) => computeValue(a(), prev), ~value=1, ());

// with options
let value = Solid.createMemo((prev) => computeValue(a(), prev), ~options=#bool({equals: false}), ());

// with unit function
let value = Solid.createMemoUnit(() => computeValue(a(), b()), ());

createResource

Originally createResource's first parameter is optional. To handle this with rescript source and options have to be passed as labeled arguments. Refetching only supports bool right now (no unknown).

let fetch = (val, _) => {
  // return a promise
}

// without source
let (data, actions) = Solid.Resource.make(fetch, ())
// with source
let (data, actions) = Solid.Resource.make(~source=() => "", fetch, ())
// with options
let (data, actions) = Solid.Resource.make(~source=() => "", fetch, ~options={initialValue: "init"} ())
// with initialValue. No explicit handling of option<> type necessary for data()
let (data, actions) = Solid.Resource.makeWithInitial(~source=() => "", fetch, ~options={initialValue: "init"} ())

Events (e.g. onClick)

Solid offers an optimized array-based alternative to adding normal event listeners. In order to support this syntax a wrapper function Event.asArray has to be used.

// solid's special array syntax
<button onClick={Solid.Event.asArray((s => Js.log(s), "Hello"))}>
  {"Click Me!"->React.string}
</button>

// normal event syntax
<button  onClick={e => Js.log("Hello")}>
  {"Click Me!"->React.string}
</button>

Lifecycles

All lifecycle functions are supported.

Reactive Utilities

Most utilities are supported.

mergeProps

ReScript does not offer the same flexibility for structural types as TypeScript does. The mergeProps function accepts any type without complaint, but it only works with records and objects. Also the compiler will have a hard time figuring out the correct type of the return value.

It is very easy to build breakable code with this function. Use with caution!

type first = {first: int}
type second = {second: string}
let merged = Solid.mergeProps({first: 1}, {second: ""})

splitProps

Supported but untested. The original function expects an arbitrary number of parameters. In ReScript we have different functions splitPropsN to model that.

This function also easily breaks your code if used incorrectly!

let split = Solid.splitProps2({first: 1, second: ""}, ["first"], ["second"])

Stores

The createStore function is called Solid.Store.make, since this is a more idiomatic naming for ReScript.

let (state, setState) = Solid.Store.make({greeting: "Hello"})

Solid's setState supports numerous practical ways to update the state. Since the function is so overloaded it is very hard to create bindings for it. Currently only the basic function syntax is supported.

setState(state => {greeting: state.greeting ++ "!"})

unwrap

let untracked = Solid.Store.unwrap(state)

Component APIs

All Component APIs are supported.

lazy

Getting dynamic imports to work with ReScript is tricky, since ReScript works completely without explicit import statements. For it to work, the "in-source": true option in bsconfig.json should be used and the generated bs.js file needs to be referenced within the import.

The Solid.Lazy.make function returns a component, that requires to be wrapped in a module. Note that this can only be used inside a function (or component) and not on the top level of a file.

Currently only components without any props can be imported.

@react.component
let make = () => {
  let module(Comp) = Solid.Lazy.make(() => Solid.import_("./Component.bs.js"))
  <Solid.Suspense fallback={"Loading..."->React.string}><Comp /></Solid.Suspense>
}

Context

createContext always requires a defaultValue. Also ReScript requires all components to start with an uppercase letter, but the object returned by createContext requires lowercase. In order to create the Provider component module(Provider) has to be used.

let context = Solid.Context.make((() => "", _ => ()))

module TextProvider = {
  @react.component
  let make = (~children) => {
    let module(Provider) = context.provider
    
    let signal = Solid.createSignal("initial", ())

    <Provider value={signal}> {children} </Provider>
  }
}
module Nested = {
  @react.component
  let make = () => {
    let (get, set) = Solid.Context.useContext(context)
    set(p => p ++ "!")
    <div> {get()->React.string} </div>
  }
}

@react.component
let make = () => <TextProvider><Nested /></TextProvider>

Secondary Primitives

All are supported. createSelector is untested.

createReaction

let (get, set) = Solid.createSignal("start", ())
let track = Solid.createReaction(() => Js.log("something"))
track(() => get()->ignore)

Rendering

render is working. All other functions are completely untested und might not work.

render

Attaches the root component to the DOM.

Solid.render(() => <App />, Document.querySelector("#root")->Belt.Option.getExn, ())

// or with dispose
let dispose = Solid.render(() => <App />, Document.querySelector("#root")->Belt.Option.getExn)

DEV

Is named dev in rescript, and treated as bool.

Control Flow

These are the regular bindings for the babel-transform variant. The HyperScript variants have their own module Solid.H (see below).

For

<Solid.For each={["Arya", "Jon", "Brandon"]} fallback={<div> {"Loading..."->React.string} </div>}>
  {(item, _) => <div> {`${item} Stark`->React.string} </div>}
</Solid.For>

Show

SolidJs' Show can be used with any truthy or falsy (like null) value. The concept of a truthy value does not translate well to ReScript, so instead Show expects an option<'t>.

<Solid.Show.Option \"when"={Some({"greeting": "Hello!"})} fallback={<div> {"Loading..."->React.string} </div>}>
  {item => <div> {item["greeting"]->React.string} </div>}
</Solid.Show.Option>

In those cases where the when clause contains an actual bool a different version of Show has to be used:

<Solid.Show.Bool \"when"={something > 0} fallback={<div> {"Loading..."->React.string} </div>}>
   <div> {"Hello!"->React.string} </div>
</Solid.Show.Bool>

Index

<Solid.Index each={["Arya", "Jon", "Brandon"]} fallback={<div> {"Loading..."->React.string} </div>}>
  {(item, _) => <div> {`${item()} Stark`->React.string} </div>}
</Solid.Index>

Switch/Match

Match supports the same Variants (Bool, Option) as Show.

<Solid.Switch fallback={"Fallback"->React.string}>
  <Solid.Match.Bool \"when"={false}>
    {"First match"->React.string} 
  </Solid.Match.Bool>
  <Solid.Match.Option \"when"={Some("Second match")}>
    {text => text->React.string}
  </Solid.Match.Option>
</Solid.Switch>

ErrorBoundary

Only the variant with a fallback function is supported.

<Solid.ErrorBoundary fallback={(_, _) => <div> {"Something went terribly wrong"->React.string} </div>}>
  <MyComp />
</Solid.ErrorBoundary>

Suspense

<Solid.Suspense fallback={<div> {"Loading..."->React.string} </div>}> <AsyncComp /> </Solid.Suspense>

Special JSX Attributes

Custom directives are not supported.

ref

Refs require function syntax.

@react.component
let make = () => {
  let myRef = ref(Js.Nullable.null)

  <div ref={el => {myRef := el}} />
}

classList

classList behaves differently. Instead of an object it uses tuples of (string, bool). It uses a thin wrapper to convert the tuples into an object.

<div classList={Solid.makeClassList([("first", val() == 0), ("other", val() != 0)])} />

style

style only supports string syntax right now.

<div style={`background-color: green; height: 100px`} />

on...

See Events section above.

Examples

Please check the examples folder for a complete project configured with ReScript, solidJs and vite.

Missing features

For these features no bindings exist yet.

• observable
• from
• produce
• reconcile
• createMutable
• all stuff related to hydration is untested
• Dynamic
• custom directives
• /_ @once _/

Usage of HyperScript variant

The first version of this library used HyperScript as bridge between ReScript and solidJs. Although the bindings for both variants are almost identical, there are two differences to note:

1. For HyperScript to be reactive, every prop and child has to be wrapped in a function.
2. For, Show and Index versions for HyperScript are in their own module (Solid.H)

Installation

We have to trick ReScript to accept this library as a replacement for the original react bindings. This can be accomplished by using a module alias.

Install with npm:

npm install solid-js @fattafatta/rescript-solidjs react@npm:@fattafatta/rescript-solidjs

Or install with yarn:

yarn add solid-js @fattafatta/rescript-solidjs react@npm:@fattafatta/rescript-solidjs

Add @fattafatta/rescript-solidjs as a dependency to your bsconfig.json:

"bs-dependencies": ["@fattafatta/rescript-solidjs"]

Make sure to remove @rescript/react if it is already listed. It is impossible to use this library and the original react binding together.

Reactivity with HyperScript

solidJs' HyperScript requires that all reactive props and children are wrapped in a function (unit => 'returnValue). But adding those functions would completely mess up the ReScript type system. The solution is to wrap any reactive code with the Solid.track() function. (This function adds no additional overhead and will be removed by the complier. It's only purpose is to make the types match.)

// GOOD
{Solid.track(() => (count()->React.int))}

// BAD, this count would never update
{count()->React.int}

Control flow with HyperScript

The necessary HyperScript bindings for Show, For and Index are all encapsulated in the module Solid.H. These helper components always expect reactive syntax (e.g. props have to we wrapped in () => 'a). Therefore it is not necessary to wrap the each or when with a track.

Example for For:

<Solid.H.For each={() => ["Arya", "Jon", "Brandon"]} fallback={<div> {"Loading..."->React.string} </div>}>
  {(item, _) => <div> {`${item} Stark`->React.string} </div>}
</Solid.H.For>

Example for Show:

<Solid.H.Show.Option \"when"={() => Some({"greeting": "Hello!"})} fallback={<div> {"Loading..."->React.string} </div>}>
  {item => <div> {item["greeting"]->React.string} </div>}
</Solid.H.Show.Option>

Acknowledgments

This library used multiple sources for inspiration. Especially https://github.com/woeps/solidjs-rescript was of great help to get the initial version going. It proved that ReScript and solidJs could work together when using HyperScript. The only missing step was to make the ReScript compiler produce HyperScript, to that JSX would work too.

Additional info

Discussion about ReScript on github: https://github.com/solidjs/solid/discussions/330#discussioncomment-339972

Discussion about solidJs in the ReScript forums: https://forum.rescript-lang.org/t/change-jsx-output-from-react-to-solidjs/1930/12