tamda/dist/function/infer.js

Practical functional programming library for TypeScript

/**
 * Creates a function that can infer the first argument according to the number of supplied arguments.
 *
 * If all arguments are supplied, immediately invokes the function.
 * Otherwise, return a function that expects the first argument of the original function.
 *
 * @param ready Optionally determine when a function is ready for execution.
 * Default `args.length >= fn.length`.
 *
 * @example
 * const map = (array, fn) => array.map(fn);
 * const inferredMap = infer(map);
 * inferredMap([1, 2, 3], n => n + 1);
 * // [2, 3, 4]
 * inferredMap (n => n + 1) ([1, 2, 3]);
 * // [2, 3, 4]
 *
 * Useful for composing/piping, e.g.
 *
 * const transform = pipe(
 *  map(n => n + 1),
 *  map(n => n * 2),
 *  filter(n => n > 5)
 * );
 * transform([1, 2, 3]);
 * // [6, 8]
 */
export function infer(fn, ready = isReady(fn)) {
    // tslint:disable-next-line: only-arrow-functions
    return function () {
        // faster than spread, i.e. (...args: unknown[]) => {}
        const args = arguments;
        return ready(args)
            ? fn.apply(undefined, args)
            : (first) => fn(first, ...args);
    };
}
const isReady = (fn) => (args) => args.length >= fn.length;
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