Web3.Ui.RemoteCall

The remote-data type for correlation-id port round-trips -- the missing foundation under every read in a dapp.

Every elm-web3 read (balance, contract call, fee, block...) is fire-and-forget through a port, matched back by a correlation id. Modelling each one by hand means every dapp reinvents Maybe (Result String a) plus an in-flight flag plus id bookkeeping. RemoteCall is that shape, once, with the id bookkeeping built in:

type alias Model =
    { reserves : RemoteCall Reserves }


-- fire
( { model | reserves = RemoteCall.request "reserves-1" model.reserves }
, web3Cmd (Call.encode reservesCall)
)


-- resolve (ONLY applies if the id matches the one in flight --
-- a stale response for an earlier request cannot clobber a newer one)
{ model | reserves = RemoteCall.resolve incomingId result model.reserves }


-- render
RemoteCall.view
    { skeleton = Skeleton.line []
    , failed = \\err -> Html.text err
    }
    viewReserves
    model.reserves

The id guard follows the same rule the Web3.Sign machine proves in elm-web3's SignSpec.tla: a response for a different correlation id never completes the pending call.

type RemoteCall a

= NotAsked

| Loading String

| Ready a

| Failed String

The four honest states of a port round-trip. Loading carries the correlation id of the request in flight.

notAsked : RemoteCall a

The initial state.

request : String -> RemoteCall a -> RemoteCall a

Mark a request in flight under the given correlation id. Always transitions -- firing a new request supersedes whatever came before, and its id becomes the only one resolve will accept.

resolve : String -> Result String a -> RemoteCall a -> RemoteCall a

Apply a response -- but only if its correlation id matches the request in flight. A stale or misrouted response (an earlier request answered late, another component's id) is dropped on the floor, never shown as fresh data.

reset : RemoteCall a -> RemoteCall a

Back to NotAsked (e.g. on wallet disconnect or chain switch, when the data no longer describes anything).

map : (a -> b) -> RemoteCall a -> RemoteCall b

Transform the value inside Ready.

withDefault : a -> RemoteCall a -> a

The value, or a fallback.

toMaybe : RemoteCall a -> Maybe a

Just the value when Ready.

isLoading : RemoteCall a -> Bool

True while a request is in flight.

correlationId : RemoteCall a -> Maybe String

The correlation id in flight, if any.

view : Slots msg -> (a -> Html msg) -> RemoteCall a -> Html msg

Render a RemoteCall, wrapped in a <div class="web3-remote"> whose modifier tracks the state -- --loading carries aria-busy="true" so assistive tech knows the region is settling.

CSS classes: web3-remote, web3-remote--loading, web3-remote--ready, web3-remote--failed.

type alias Slots msg =

{ skeleton : Html msg

, failed : String -> Html msg

}

What to render for the non-Ready states. NotAsked renders the skeleton too -- from the user's point of view "not fetched yet" and "fetching" look the same.

intrepidshape/elm-web3-ui/2.4.0

Web3.Ui.RemoteCall

Modules