107 lines
2.6 KiB
JavaScript
107 lines
2.6 KiB
JavaScript
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/*
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* Quick-n-dirty algebraic datatypes.
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*
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* These let us handle the possibility of failure without having to constantly write code to check for it.
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* We can apply all of the transformations we need as if the data is present using `map`.
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* If there's a None, or a FetchError, or a Pending, those are left untouched.
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*
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* I've used perhaps an odd bit of terminology from scalaz in `fold`. This is basically a `switch` statement:
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* You pass it a set of functions to handle the various different states of the datatype, and if it finds the
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* function it'll call it on its value.
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*
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* It's handy to have this in functional style when dealing with React as we can dispatch different ways of rendering
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* really simply:
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* ```
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* bundleFetchStatus.fold({
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* some: (fetchStatus) => <ProgressBar fetchsStatus={fetchStatus} />,
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* }),
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* ```
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*/
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class Optional {
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static from(value) {
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return (value && Some.of(value)) || None;
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}
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map(f) {
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return this;
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}
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flatMap(f) {
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return this;
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}
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fold({ none }) {
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return none && none();
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}
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}
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class Some extends Optional {
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constructor(value) {
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super();
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this.value = value;
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}
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map(f) {
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return Some.of(f(this.value));
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}
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flatMap(f) {
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return f(this.value);
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}
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fold({ some }) {
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return some && some(this.value);
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}
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static of(value) {
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return new Some(value);
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}
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}
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const None = new Optional();
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class FetchStatus {
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constructor(opt = {}) {
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this.opt = { at: Date.now(), ...opt };
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}
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map(f) {
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return this;
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}
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flatMap(f) {
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return this;
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}
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}
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class Success extends FetchStatus {
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static of(value) {
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return new Success(value);
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}
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constructor(value, opt) {
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super(opt);
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this.value = value;
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}
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map(f) {
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return new Success(f(this.value), this.opt);
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}
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flatMap(f) {
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return f(this.value, this.opt);
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}
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fold({ success }) {
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return success instanceof Function ? success(this.value, this.opt) : undefined;
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}
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}
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class Pending extends FetchStatus {
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static of(opt) {
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return new Pending(opt);
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}
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constructor(opt) {
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super(opt);
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}
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fold({ pending }) {
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return pending instanceof Function ? pending(this.opt) : undefined;
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}
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}
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class FetchError extends FetchStatus {
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static of(reason, opt) {
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return new FetchError(reason, opt);
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}
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constructor(reason, opt) {
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super(opt);
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this.reason = reason;
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}
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fold({ error }) {
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return error instanceof Function ? error(this.reason, this.opt) : undefined;
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}
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}
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