fn() if resA is an Ok.
import { andThen, err, ok, Result } from "./result.ts";
import { assertEquals } from "../deps.ts";
const sqrtThenToString = andThen(
(num: number): Result<string, string> =>
num < 0
? err("num must not be negative")
: ok(Math.sqrt(num).toString()),
);
assertEquals(sqrtThenToString(ok(4)), ok("2"));
assertEquals(sqrtThenToString(ok(-1)), err("num must not be negative"));
assertEquals(sqrtThenToString(err("not a number")), err("not a number"));
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Returns
fn(v)ifresAis anOk(v), otherwise returns the errorresA. This is an implementation ofFlatMap. The order of arguments is reversed because of that it is useful for partial applying.