使用fp-ts sequenceT时如何"widen" reader打字？

Question

我想知道在使用 sequenceT 时是否可以“加宽”我的最终 Reader 类型？这在使用 chainW 等顺序链接操作时是可能的，但看起来在使用 sequenceT 时你被困在每个项目都必须使用相同的 Reader 类型。我想这样做，这样我就可以在适当的时候并行执行一些任务，但仍然可以通过 Reader.

使用依赖注入

示例：

import { sequenceT } from 'fp-ts/lib/Apply'
import { log } from 'fp-ts/lib/Console'
import { pipe } from 'fp-ts/lib/function'
import * as RT from 'fp-ts/ReaderTask'

interface Person {
  name: string
}

const getMe = (name: string) => (deps: { api: any }) => async (): Promise<Person> => {
  const person = {
    name,
  }
  return person
}

const getMum = (child: Person) => (deps: { api2: any }) => async (): Promise<Person> => {
  const person = {
    name: child.name + "'s mum",
  }
  return person
}

const getDad = (child: Person) => (deps: { api2: any }) => async (): Promise<Person> => {
  const person = {
    name: child.name + "'s dad",
  }
  return person
}

const getFamily = (name: string) => 
  pipe(
    getMe(name),
    RT.chainW(me => 
      sequenceT(RT.readerTask)(
        getMum(me), 
        getDad(me))
    ))

getFamily('John')({ api: 'x', api2: 'y' })().then(
  ([mum, dad]) => {
    log(mum)()
    log(dad)()
  })

这可以很好地编译并输出：

$ node dist/src/index.js
{ name: "John's mum" }
{ name: "John's dad" }

现在假设 getDad 依赖于不同的 api，比如 api3。如果我更新它不再编译的代码，因为 getMum 和 getDad 没有使用相同的 Reader 类型。

示例（不编译）：

import { sequenceT } from 'fp-ts/lib/Apply'
import { log } from 'fp-ts/lib/Console'
import { pipe } from 'fp-ts/lib/function'
import * as RT from 'fp-ts/ReaderTask'

interface Person {
  name: string
}

const getMe = (name: string) => (deps: { api: any }) => async (): Promise<Person> => {
  const person = {
    name,
  }
  return person
}

const getMum = (child: Person) => (deps: { api2: any }) => async (): Promise<Person> => {
  const person = {
    name: child.name + "'s mum",
  }
  return person
}

const getDad = (child: Person) => (deps: { api3: any }) => async (): Promise<Person> => {
  const person = {
    name: child.name + "'s dad",
  }
  return person
}

const getFamily = (name: string) => 
  pipe(
    getMe(name),
    RT.chainW(me => 
      sequenceT(RT.readerTask)(
        getMum(me), // compiler complains here
        getDad(me))
    ))

getFamily('John')({ api: 'x', api2: 'y', api3: 'z' })().then( // compiler complains here, on api3
  ([mum, dad]) => {
    log(mum)()
    log(dad)()
  })

我实际上是用 StateReaderTaskEither 来尝试这个，但简化它以使用 ReaderTask 这个例子 - 然而 sequenceT 也表现出相同的限制。

有什么解决办法吗？

Answer 1

我在多读了一些 fp-ts 代码后想出了这个。我想出的答案是只执行 sequenceT 手动有效执行的操作。

这是我的解决方案：

import { log } from 'fp-ts/lib/Console'
import { pipe } from 'fp-ts/lib/function'
import * as RT from 'fp-ts/ReaderTask'

interface Person {
  name: string
}

const getMe = (name: string) => (deps: { api: any }) => async (): Promise<Person> => {
  const person = {
    name,
  }
  return person
}

const getMum = (child: Person) => (deps: { api2: any }) => async (): Promise<Person> => {
  const person = {
    name: child.name + "'s mum",
  }
  return person
}

const getDad = (child: Person) => (deps: { api3: any }) => async (): Promise<Person> => {
  const person = {
    name: child.name + "'s dad",
  }
  return person
}

const getFamily = (name: string) => 
  pipe(
    getMe(name),
    RT.chainW(me => 
      pipe(
        RT.of((mum: Person) => (dad: Person) => [mum, dad]),
        RT.apW(getMum(me)),
        RT.apW(getDad(me))
      )
    ))

getFamily('John')({ api: 'x', api2: 'y', api3: 'z' })().then(
  ([mum, dad]) => {
    log(mum)()
    log(dad)()
  })

Answer 2

这正是 Reader/ReaderTask/ReaderTaskEither.local 的用途！我经常使用这个。例如，如果您正在并行化对 API 的 HTTP 调用，其中一些需要 auth token + base URL，而另一些只需要 base URL（所以有些使用 interface Auth { token:string, baseUrl: string } 而其他人使用 interface NoAuth { baseUrl: string }.

  interface Apis {
    java: JavaRepository,
    db: DbRepository,
    redis: RedisRepository,
  }
  interface DomainError {}

  declare const javaApiCall: RTE<JavaRepository, DomainError, JavaResult>
  declare const dbApiCall: RTE<DbRepository, DomainError, DbResult>
  declare const redisApiCall: RTE<RedisRepository, DomainError, RedisResult>
  declare const apis: Apis

  const getJava = (apis:Apis) => apis.java
  const getDb = (apis:Apis) => apis.db
  const getRedis = (apis:Apis) => apis.redis

  sequenceT(readerTaskEither)(
    RTE.local(getJava)(javaApiCall),
    RTE.local(getDb)(dbApiCall),
    RTE.local(getRedix)(redisApiCall),
  )(apis) // TaskEither<DomainError, [JavaResult,DbResult,RedisResult]>

使用fp-ts sequenceT时如何"widen" reader打字？

How to "widen" reader type when using fp-ts sequenceT?

functional-programming

typescript

fp-ts