Function: andThen()
Call Signature
andThen<
T,E,R>(thenFn,result):Result<OkFor<R>,E|ErrFor<R>>
Apply a function to the wrapped value if Ok and return a new Ok containing the resulting value; or if it is Err return it unmodified.
This differs from map in that thenFn returns another Result. You can use andThen to combine two functions which both create a Result from an unwrapped type.
You may find the .then method on an ES6 Promise helpful for comparison: if you have a Promise, you can pass its then method a callback which returns another Promise, and the result will not be a nested promise, but a single Promise. The difference is that Promise#then unwraps all layers to only ever return a single Promise value, whereas Result.andThen will not unwrap nested Results.
This is is sometimes also known as `bind`, but *not* aliased as such
Examples
import { ok, err, andThen, toString } from 'true-myth/result';
const toLengthAsResult = (s: string) => ok(s.length);
const anOk = ok('just a string');
const lengthAsResult = andThen(toLengthAsResult, anOk);
console.log(toString(lengthAsResult)); // Ok(13)
const anErr = err(['srsly', 'whatever']);
const notLengthAsResult = andThen(toLengthAsResult, anErr);
console.log(toString(notLengthAsResult)); // Err(srsly,whatever)Type Parameters
T
T
The type of the value wrapped in the Ok of the Result.
E
E
The type of the value wrapped in the Err of the Result.
R
R extends AnyResult
Parameters
thenFn
(t) => R
The function to apply to the wrapped T if maybe is Just.
result
Result<T, E>
The Maybe to evaluate and possibly apply a function to.
Returns
Result<OkFor<R>, E | ErrFor<R>>
Call Signature
andThen<
T,E,R>(thenFn): (result) =>Result<OkFor<R>,E|ErrFor<R>>
Apply a function to the wrapped value if Ok and return a new Ok containing the resulting value; or if it is Err return it unmodified.
This differs from map in that thenFn returns another Result. You can use andThen to combine two functions which both create a Result from an unwrapped type.
You may find the .then method on an ES6 Promise helpful for comparison: if you have a Promise, you can pass its then method a callback which returns another Promise, and the result will not be a nested promise, but a single Promise. The difference is that Promise#then unwraps all layers to only ever return a single Promise value, whereas Result.andThen will not unwrap nested Results.
This is is sometimes also known as `bind`, but *not* aliased as such
Examples
import { ok, err, andThen, toString } from 'true-myth/result';
const toLengthAsResult = (s: string) => ok(s.length);
const anOk = ok('just a string');
const lengthAsResult = andThen(toLengthAsResult, anOk);
console.log(toString(lengthAsResult)); // Ok(13)
const anErr = err(['srsly', 'whatever']);
const notLengthAsResult = andThen(toLengthAsResult, anErr);
console.log(toString(notLengthAsResult)); // Err(srsly,whatever)Type Parameters
T
T
The type of the value wrapped in the Ok of the Result.
E
E
The type of the value wrapped in the Err of the Result.
R
R extends AnyResult
Parameters
thenFn
(t) => R
The function to apply to the wrapped T if maybe is Just.
Returns
(
result):Result<OkFor<R>,E|ErrFor<R>>
Parameters
result
Result<T, E>
Returns
Result<OkFor<R>, E | ErrFor<R>>