[question] Why Are there Different Definitions of Models?

[VizorKit]

label:question Sorry, I'm new to purescript. I'm curious why we define 2 different models. It states that one is passed to the ffi. I transpiled each of these definitions to javascript, and only the first one exists. however, the first one appears to be a valid state to pass to the ffi method. Is there something in purescript that states we should do this, whats the reason?

type PoolConfiguration =
    { database :: Database
    , host :: Maybe String
    , idleTimeoutMillis :: Maybe Int
    , max :: Maybe Int
    , password :: Maybe String
    , port :: Maybe Int
    , user :: Maybe String
    }

-- | Configuration which we actually pass to FFI.
type PoolConfiguration' =
    { user :: Nullable String
    , password :: Nullable String
    , host :: Nullable String
    , port :: Nullable Int
    , database :: String
    , max :: Nullable Int
    , idleTimeoutMillis :: Nullable Int
    }

[Kamirus]

As users, we use PoolConfiguration, but when this config needs to be passed to the underlying js library we don't want values of type Maybe there.

Starting from the line linked below: https://github.com/rightfold/purescript-postgresql-client/blob/680da31ee1c6430fe296788994fe029024c75ade/src/Database/PostgreSQL.purs#L84 is a function which performs this transformation from PoolConfiguration to PoolConfiguration' and then calls the FFI function ffiNewPool

Record of type PoolConfiguration' is a valid object in javascript, because PureScript's records are just js objects with keys as labels. But for example Maybe String is not represented as a string or null (feel free to call unsafeStringify to see for yourself), whereas Nullable has this exact runtime representation that is suitable for FFI functions

[VizorKit]

Cool, thank you. This does make sense, maybe in more time I would see the reason as to why would we even use Maybe over Nullable in purescript. For now I can go with it. I'm sorry I chose this project to work with purescript and figure out the complex parts with Aff, Effect, FFI, etc. If you want me to go somewhere else I can.

[Kamirus]

Awesome :smile: You can check out the forum, here is the link to the specific thread with a repo you might be interested in https://discourse.purescript.org/t/purescript-ffi-best-practices/1081, and there's more if you search for 'FFI'. And there's more knowledge regarding Aff, Effect and FFI in PS on the internet, you can ask someone on slack