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Tagless Final example with fp-ts
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import { HKT, Type, URIS } from 'fp-ts/lib/HKT'; | |
import { identity, Identity, URI } from 'fp-ts/lib/Identity'; | |
import { Monad, Monad1 } from 'fp-ts/lib/Monad'; | |
// Task: get all users named 'John' and make them admins | |
interface User { | |
id: number; | |
name: string; | |
age: number; | |
isAdmin: boolean; | |
} | |
const fakeUsers: User[] = [ | |
{ | |
id: 1, | |
name: 'John Connor', | |
age: 32, | |
isAdmin: false, | |
}, | |
{ | |
id: 2, | |
name: 'John Smith', | |
age: 18, | |
isAdmin: false, | |
}, | |
{ | |
id: 3, | |
name: 'Mark Brian', | |
age: 28, | |
isAdmin: false, | |
}, | |
]; | |
interface UserOps<M> { | |
search: (params: Partial<User>) => HKT<M, User[]>; | |
makeAdmins: (users: User[]) => HKT<M, User[]>; | |
save: (users: User[]) => HKT<M, boolean[]>; | |
} | |
interface UserOps2<M extends URIS> { | |
search: (params: Partial<User>) => Type<M, User[]>; | |
makeAdmins: (users: User[]) => Type<M, User[]>; | |
save: (users: User[]) => Type<M, boolean[]>; | |
} | |
interface App<M> extends UserOps<M>, Monad<M> { } | |
interface App2<M extends URIS> extends UserOps2<M>, Monad1<M> { } | |
interface Program { | |
getMain<M extends URIS>(M: App2<M>): () => Type<M, boolean[]>; | |
} | |
class Program { | |
getMain<M>(M: App<M>): () => HKT<M, boolean[]> { | |
return () => { | |
const johns = M.search({ name: 'John' }); | |
const admins = M.chain(johns, M.makeAdmins); | |
return M.chain(admins, M.save); | |
}; | |
} | |
} | |
const testInstance: App2<URI> = { | |
...(identity as Monad1<URI>), | |
search: (params: Partial<User>) => identity.of(fakeUsers.filter((u) => u.name.includes(params.name))), | |
makeAdmins: (users: User[]) => identity.of(users.map((u) => ({ ...u, isAdmin: true }))), | |
save: (users: User[]) => identity.of(users.map((u) => u.isAdmin)), | |
}; | |
const main = new Program().getMain(testInstance); | |
const result = main() as Identity<boolean[]>; | |
console.log(result.value); |
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