Effect.gen

pipelineでも書けるが、手続き的にEffectの組み合わせ処理を書ける

code:ts

import { Effect } from "effect"

// Function to add a small service charge to a transaction amount

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

// Function to apply a discount safely to a transaction amount

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)) // Effect.Effect<number, never, never>

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

code:ts

// Assembling the program using a generator function

const program = Effect.gen(function* () {

const transactionAmount = yield* fetchTransactionAmount // number

const discountRate = yield* fetchDiscountRate

const discountedAmount = yield* applyDiscount(

transactionAmount,

discountRate

)

const finalAmount = addServiceCharge(discountedAmount)

})

// Execute the program and log the result

Effect.runPromise(program).then(console.log)

// Output: Final amount to charge: 96

code:ts

class MyClass {

readonly local = 1

compute = Effect.gen(this, function* () {

const n = this.local + 1

return n

})

}