Effect CommunityEC
Effect Community•13mo ago•
2 replies
AndersR

How does one pass argument values to Effect.gen?

In a pipeline I can initiate that pipe with some initial input value. How would I do the equivalent with a generator flow? All the examples in the docs (https://effect.website/docs/getting-started/using-generators/) have hard-coded input values. What would be an example of passing in a variable? For example, in the docs we have this:

import { Effect } from "effect"

const addServiceCharge = (amount: number) => amount + 1

const applyDiscount = (
  total: number,
  discountRate: number
): Effect.Effect<number, Error> =>
  discountRate === 0
    ? Effect.fail(new Error("Discount rate cannot be zero"))
    : Effect.succeed(total - (total * discountRate) / 100)

const fetchTransactionAmount = Effect.promise(() => Promise.resolve(100))

const fetchDiscountRate = Effect.promise(() => Promise.resolve(5))

export const program = Effect.gen(function* () {
  const transactionAmount = yield* fetchTransactionAmount
  const discountRate = yield* fetchDiscountRate
  const discountedAmount = yield* applyDiscount(
    transactionAmount,
    discountRate
  )
  const finalAmount = addServiceCharge(discountedAmount)
  return `Final amount to charge: ${finalAmount}`
})


As you can see, here the transaction amount is hard-coded. What if I wanted to be able to pass in that value as a variable? Btw, this all feels very basic so I am wondering if there is something fundamental I am missing here. Thanks for any insights!
Effect Documentation
Using Generators
Learn how to use generators in Effect for writing effectful code, enhancing control flow, handling errors, and simplifying asynchronous operations with a syntax similar to async/await.
Using Generators
Was this page helpful?