option-t/esm/nullable/operators/and_then.js

A toolkit of Nullable/Option/Result type implementation in ECMAScript. Their APIs are inspired by Rust's `Option<T>` and `Result<T, E>`.

import { isNull } from '../core/nullable.js';
/**
 *  Returns `null` if the _input_ is `null`,
 *  otherwise calls _transformer_ with the value and returns the result.
 *
 *  XXX:
 *  Some languages call this operation flatmap.
 *  But we don't provide `flatMap()` as alias of this function.
 *  because it's too hard to undarstand that "flatMap" operation for `T | null`
 */
export function andThenForNullable(input, transformer) {
    if (isNull(input)) {
        return input;
    }
    const result = transformer(input);
    return result;
}