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December 22, 2023 04:13
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fp-ts sample
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| import { pipe } from 'fp-ts/function'; | |
| import * as O from 'fp-ts/Option'; | |
| import * as E from 'fp-ts/Either'; | |
| import * as A from 'fp-ts/Array'; | |
| import { sequenceT } from 'fp-ts/Apply'; | |
| import { flow } from 'fp-ts/function'; | |
| import * as t from 'io-ts'; | |
| // Example of a complex validator using io-ts | |
| const UserProfile = t.type({ | |
| name: t.string, | |
| age: t.Int, // Int is a refinement of number which ensures it's an integer | |
| email: t.string, | |
| }); | |
| // Let's assume we have some user input that needs validation | |
| const userInput = { | |
| name: 'Alice', | |
| age: 30, | |
| email: 'alice@example.com', | |
| }; | |
| // Function to simulate an API call that might fail | |
| function fetchUserFromAPI(userId: number): E.Either<Error, unknown> { | |
| return Math.random() > 0.5 | |
| ? E.right({ name: 'Bob', age: 28, email: 'bob@example.com' }) | |
| : E.left(new Error('Failed to fetch user')); | |
| } | |
| // Function to validate user data with io-ts | |
| function validateUser(input: unknown): E.Either<t.Errors, t.TypeOf<typeof UserProfile>> { | |
| return UserProfile.decode(input); | |
| } | |
| // Helper function to transform Either to Option | |
| const eitherToOption = <E, A>(e: E.Either<E, A>): O.Option<A> => | |
| pipe( | |
| e, | |
| E.fold( | |
| (_, __) => O.none, | |
| (a) => O.some(a) | |
| ) | |
| ); | |
| // Simulate fetching multiple users and validating them | |
| const userIds = [1, 2, 3, 4]; | |
| const validatedUsers = pipe( | |
| userIds, | |
| A.map(fetchUserFromAPI), | |
| A.map(eitherToOption), | |
| A.compact, // Remove None values | |
| A.map(validateUser) | |
| ); | |
| // Function to combine several Options into one | |
| const combineOptions = sequenceT(O.Apply); | |
| // Example of using combinators to process data (e.g., finding users over 25) | |
| const findUsersOver25 = (users: Array<E.Either<t.Errors, t.TypeOf<typeof UserProfile>>>): Array<t.TypeOf<typeof UserProfile>> => | |
| pipe( | |
| users, | |
| A.map(E.fold( | |
| () => [], | |
| (user) => user.age > 25 ? [user] : [] | |
| )), | |
| A.flatten | |
| ); | |
| // Using the functions to process the user data | |
| const result = pipe( | |
| validatedUsers, | |
| (users) => findUsersOver25(users) | |
| ); | |
| // Showcasing advanced composition using fp-ts | |
| const processUserData = flow( | |
| A.map(fetchUserFromAPI), | |
| A.map(eitherToOption), | |
| A.compact, | |
| A.map(validateUser), | |
| findUsersOver25 | |
| ); | |
| // Process the list of userIds | |
| const finalResult = processUserData(userIds); | |
| // Print out the results of our operations | |
| console.log('Validated Users:', JSON.stringify(result, null, 2)); | |
| console.log('Final Result:', JSON.stringify(finalResult, null, 2)); |
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