FP list combinators demo with fp-ts

README.md

tsc && node main.js

main.ts

import { catOptions, array } from 'fp-ts/lib/Array';
import { sequence, traverse } from 'fp-ts/lib/Traversable';
import { Option, some, none, option } from 'fp-ts/lib/Option';

{
    //
    // catOptions
    // <T>(options: Array<Option<T>>) => Option<T>
    //

    const nameMaybes = [some('foo'), some('bar'), none];
    const names = catOptions(nameMaybes);

    console.log({ names });
    // { names: [ 'foo', 'bar' ] }
}

{
    //
    // sequenceOptions
    // <T>(options: Array<Option<T>>) => Option<Array<T>>
    //

    const sequenceOptions = sequence(option, array);

    const nameMaybes1 = [some('foo'), some('bar'), none];
    const maybeNames1 = sequenceOptions(nameMaybes1);
    console.log({ maybeNames1 });
    // { maybeNames1: none }

    const nameMaybes2 = [some('foo'), some('bar'), some('baz')];
    const maybeNames2 = sequenceOptions(nameMaybes2);
    console.log({ maybeNames2 });
    // { maybeNames2: some(["foo", "bar", "baz"]) }
}

type Person = { name: Option<string> };

const people1 = [{ name: some('foo') }, { name: some('bar') }, { name: none }];
const people2 = [
    { name: some('foo') },
    { name: some('bar') },
    { name: some('baz') },
];

const getName = (person: Person) => person.name;

{
    //
    // traverseOptions
    // <A, B>(as: Array<A>, transform: (a: A) => Option<B>) => Option<Array<B>>
    //

    const traverseOptions = traverse(option, array);

    const maybeNames1 = traverseOptions(people1, getName);
    console.log({ maybeNames1 });
    // { maybeNames1: none }
    const maybeNames2 = traverseOptions(people2, getName);
    console.log({ maybeNames2 });
    // { maybeNames2: some(["foo", "bar", "baz"]) }
}

{
    //
    // filterMap
    // <A, B>(as: Array<A>, transform: (a: A) => Option<B>) => Array<B>
    //

    const names = array.filterMap(people1, getName);
    console.log({ names });
    // { names: [ 'foo', 'bar' ] }
}

package.json

{
  "dependencies": {
    "fp-ts": "^1.8.0",
    "typescript": "^3.0.3"
  }
}

tsconfig.json

{
    "compilerOptions": {
        "strict": true
    },
    "files": [
        "./main.ts"
    ]
}