Reaml (React + ML)
A React binding for (OCaml | ReasonML) + BuckleScript with compile time enforcement of the "Rules of Hooks" (How?).
Overview
The "Hello, World!" of Reaml looks like this:
module R = Reaml
let main = R.h1 [ R.id "hello" ] [ R.string "Hello, world!" ]
let () = main |> R.renderTo "main"
The code above renders <h1 id="hello">Hello, World!</h1>
into the first
element on the page matching the selector main
.
Note: If you want to use ReasonML syntax instead of OCaml, check out the last section for the equivalent ReasonML code.
Components are defined using a syntax extension
[@reaml.component "DisplayNameOfComponent"]
applied to let
s of one
argument functions:
module R = Reaml
module Counter = struct
type props = { initial : int }
let[@reaml.component "Counter"] make { initial } =
R.div [] [R.int initial]
end
Components are initialized using simple function calls:
let main = Counter.make { initial = 0 }
Hooks are invoked using a [@reaml]
annotation on let
expressions:
let[@reaml.component "Counter"] make { initial } =
let[@reaml] count, setCount = R.useState initial in
R.div [] [R.int initial]
Here's a full example of a Counter with two buttons, one to increment and one to decrement the value (full source):
module Counter = struct
type props = { initial : int }
let[@reaml.component "Counter"] make { initial }=
let[@reaml] count, setCount = R.useState initial in
R.div
[]
[ R.button [ R.onClick (fun _ -> setCount (count - 1)) ] [ R.string "-" ]
; R.string " "
; R.int count
; R.string " "
; R.button [ R.onClick (fun _ -> setCount (count + 1)) ] [ R.string "+" ]
]
end
Custom hooks are created using a syntax extension [@reaml.hook]
applied to
fun
s of one argument. Here's a custom hook that wraps useReducer
, invoking
any action dispatched twice instead of once.
let[@reaml.hook] useDoubleReducer (reducer, initialValue) =
let[@reaml] state, dispatch = R.useReducer reducer initialValue in
let dispatchTwice action =
dispatch action;
dispatch action
in
state, dispatchTwice
These custom hooks are called in the same manner as the built-in hooks -- using
let[@reaml]
:
let[@reaml.component "CustomHooks"] make () =
let reducer state action = state + action in
let[@reaml] state, dispatch = useDoubleReducer (reducer, 0) in
R.button [ R.onClick (fun _ -> dispatch 2) ] [ R.int state ]
Full example here.
Quick Start
$ git clone https://github.com/utkarshkukreti/reaml-starter
$ cd reaml-starter
$ yarn install
$ yarn build
This will build /src/Main.ml
into the /dist/
directory which you can run by
opening /index.html
in your browser.
Feel free to copy code from examples into src/Main.ml
and
recompile.
How are the Rules of Hooks enforced at compile time?
Reaml uses an OCaml syntax extension to enforce them.
This requires annotating components with [@reaml.component]
, custom hooks
with [@reaml.hook]
, and every use of a hook with let[@reaml]
.
For [@reaml.hook]
, the syntax extension appends a dummy argument to the
function, the value of which must be of type Reaml.undefined
(represented as
plain undefined
in JS).
For both [@reaml.hook]
and [@reaml.component]
, the syntax extension
traverses the top level let
expressions and rewrites let[@reaml]
expressions, appending the undefined
value to the function call on the right.
If you call a hook without let[@reaml]
, you will get a type check error due to
a missing argument.
After all this is done, the syntax extension traverses the whole program and checks whether any of these annotations were not processed and throws an error if it finds any because it means the annotation was incorrectly used.
For more examples, check out the files under /examples. A live demo of all the examples is available here.
ReasonML
Here's the Hello World example in ReasonML:
module R = Reaml;
let main = R.h1([R.id("hello")], [R.string("Hello, world!")]);
main |> R.renderTo("main");
Here's an example of ReasonML code which uses all the three annotations that this library uses:
module R = Reaml;
[@reaml.hook]
let useDoubleReducer = ((reducer, initialValue)) => {
let[@reaml] (state, dispatch) = R.useReducer(reducer, initialValue);
let dispatchTwice = action => {
dispatch(action);
dispatch(action);
};
(state, dispatchTwice);
};
[@reaml.component "CustomHooks"]
let make = () => {
let reducer = (state, action) => state + action;
let[@reaml] (state, dispatch) = useDoubleReducer((reducer, 0));
R.button([R.onClick(_ => dispatch(1))], [R.int(state)]);
};
let main = make();
main |> R.renderTo("main");
For more guidance on how to translate OCaml code into ReasonML, try pasting the OCaml code in the Try ReasonML page or read this guide.
License
MIT