使用 and 對 Future 執行 && 判斷 | 點燈坊

若想對 Future 執行類似 ECMAScript 的 && 判斷，可使用 and。

Version

Fluture 14.0.0

Resolved Future

import { pipe } from 'ramda'
import { resolve, fork, and } from 'fluture'
import { error, log } from 'wink-fp'

let data = resolve (1)

let f = pipe (
  and (resolve (2)),
  fork (error) (log)
)

f (data) 

若 data 為 Resolved Future 時，則回傳另一個 Future (可為 Rejected Future 或 Resolved Future)，否則回傳原 Future，此時可使用 and 判斷，類似 ECMAScript 的 &&。

and
Future a c -> Future a b -> Future a c
若為 Resolved Future，則回傳新 Future，否則回傳原 Future

• Future a c：傳入新 Future，可為 Rejected Future 或 Resolved Future
• Future a b：data 為 Future
• Future a c：回傳新 Future 或原 Future

Rejected Future

import { pipe } from 'ramda'
import { reject, resolve, fork, and } from 'fluture'
import { error, log } from 'wink-fp'

let data = reject (1)

let f = pipe (
  and (resolve (2)),
  fork (error) (log)
)

f (data) 

若 data 為 Rejected Future，則直接回傳原 Future。

Railway Oriented Programming

and 支援 Railway Oriented Programming，因為傳入可能是 Rejected Future 或 Resolved Future，因此可能切到 Rejected Track 或 Resolved Track。

Conclusion

• and 很類似 ECMAScript 的 && operator，但只適用於 Future

Reference

Aldwin Vlasbolm, Functional Alternative to Promises
Fluture, and