PureScript on Production

The Backgound

We love using Scala with Cats

API is Typed

type API = Kleisli[OptionT[F, ?], In[F], Out[F]]

to gain Type level safety

where In is Req and Out is Resp, F represent some effects which could be simply just IO

type API = Kleisli[OptionT[IO, ?], Req[IO], Resp[IO]]

if I read this loud it would be like our API is something that:

takes Req[IO] (which could has some IO happen, but not yet. i.e. there a json body)

returns Resp[IO] (which could end up with some IO ops as well)

but our API cannot handle all kind of request, some may end up with 404

so it’s OptionT[IO, Resp[IO] our API will finally got return

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No much choice of front end stack

Well in TypeScript, the only thing you can model using Type is data

export interface Company {

id: number

companyId: CompanyId

name: CompanyName

account: CompanyAccount

access: CompanyAccess

country: string

status: CompanyStatus

}

or little bit more than that: ADT

export type CompanyABN = ValidationError | ValidatedABN | EmptyABN

but in the end, we defined twice amount of LoC of such Type more than our actual Logic

most benifit is maybe

IDE works much better than JavaScript’s

and that twice amount of type could still end up run time error

let getCompany: Promise<Company> = getJSON<Company>("bank-end-url")

getJSON is actually from JS lib, so it won’t actually check the JSON response is actually able to parse into our Typed model

Backend