combine-type-predicates


Combine [user-defined type guards / type predicates][user-defined-type-guards]
as [unions][union] and [intersections][intersection].

[user-defined-type-guards]: https://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards
[union]: https://www.typescriptlang.org/docs/handbook/advanced-types.html#union-types
[intersection]: https://www.typescriptlang.org/docs/handbook/advanced-types.html#intersection-types

``ts
import { isSome, isEvery } from 'combine-type-predicates';

type Foo = { foo: boolean; baz: number };
type Bar = { bar: symbol; baz: string };

const isFoo = (v: unknown): v is Foo
=> typeof v.foo === 'boolean' && v.baz === 'number';
const isBar = (v: unknown): v is Bar
=> typeof v.bar === 'symbol' && v.baz === 'string';

const isFooOrBar = isSome(isFoo, isBar);
// => (subject: unknown) => subject is Foo | Bar

const isFooAndBar = isEvery(isFoo, isBar);
// => (subject: unknown) => subject is Foo & Bar

const x: unknown = undefined;

if (isFooOrBar(x)) {
x.baz; // => string | number

if ('foo' in x) {
x.foo; // => boolean
} else {
x.bar; // => symbol
}
}

if (isFooAndBar(x)) {
x.foo; // => boolean
x.bar; // => symbol
x.baz; // => never (no such thing as string & number)
}
``