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May 4, 2020 13:41
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Monoid Type Class Example Use Case
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| // The use cases for Monoids & Semigroups are pretty similar | |
| // Not every Semigroup can be a Monoid, e.g. when there is no neutral value for empty | |
| // An example use case for both Semigroups & Monoids | |
| // We merge two objects together we merge them by always using the right-most non-None value | |
| // We do this by using the getLastMonoid function from fp-ts | |
| // Mostly taken from https://dev.to/gcanti/getting-started-with-fp-ts-monoid-ja0 | |
| import { getStructMonoid } from "fp-ts/lib/Monoid"; | |
| import { Option } from "fp-ts/lib/Option"; | |
| interface Settings { | |
| audioQuality: Option<"High" | "Medium" | "Low">; | |
| downloadQuality: Option<"High" | "Medium" | "Low">; | |
| downloadWithoutWifi: Option<boolean>; | |
| username: Option<string>; | |
| } | |
| const monoidSettings: Monoid<Settings> = getStructMonoid({ // getStructMonoid is the same as getStructSemigroup; for more context see https://gist.github.com/Cedomic/7528477f0ee8cd8417b0bac376ffba5a | |
| audioQuality: getLastMonoid<"High" | "Medium" | "Low">(), // getLastMonoid is like getLastSemigroup and just returns the second parameter passed into the concat method from the Monoid | |
| downloadQuality: getLastMonoid<"High" | "Medium" | "Low">(), | |
| downloadWithoutWifi: getLastMonoid<boolean>(), | |
| username: getLastMonoid<string>(), | |
| }); | |
| const standardSettings: Settings = { | |
| audioQuality: some("Medium"), | |
| downloadQuality: some("Medium"), | |
| downloadWithoutWifi: some(false), | |
| username: some(getRandomString()); // getRandomString is a dummy function that will return something like "hg29dwo26&(ash" | |
| }; | |
| const userSettings: Settings = { | |
| audioQuality: some("High"), | |
| downloadQuality: none, | |
| downloadWithoutWifi: some(true), | |
| username: some("Bob"), | |
| }; | |
| // userSettings overrides standardSettings | |
| monoidSettings.concat(standardSettings, userSettings); | |
| /* | |
| { | |
| audioQuality: { _tag: 'Some', value: 'High' }, | |
| downloadQuality: { _tag: 'Some', value: 'Medium' }, | |
| downloadWithoutWifi: { _tag: 'Some', value: true }, | |
| username: { _tag: 'Some', value: 'Bob' }, | |
| } | |
| */ |
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