Verdict4s

A Scala 3 client for TypeSafe AI's Jev, a decision model that answers typed questions about your program state with choices, scores and calibrated probabilities instead of text.

You describe the decision; your code keeps control of what happens next.

val (urgent, team, mood) = client.ask(
  Ask(
    Question.noul("Does this convey urgency?"),
    Question.choice[Dept]("Which team should handle this?"),
    Question.score("How frustrated?", Seq("Calm", "Frustrated", "Very angry"))
  ),
  "Help! My payouts have been failing for 3 days."
)

urgent is a NoulAnswer, team a ChoiceAnswer[Dept], mood a ScoreAnswer — destructured positionally, at exactly the right types, with no casts and no lookups by string.

Verdict4s cross-builds for the JVM and Scala.js from the same sources and at the same version.

Why the types matter here

The service enforces real limits: a Choice takes 1 to 255 options, a Score takes 2 to 10 ordered levels, probabilities live in the unit interval. Those are carried by the types rather than discovered a network round trip later.

Probability(0.95)   // fine
Probability(1.5)    // does not compile

Questions are validated before anything is sent, and failures accumulate, so a request with three problems reports all three at once rather than one per attempt.

Choosing a module

Verdict4s is published to Maven Central for Scala 3 as three layers. Pick the one that matches how much you want the library to decide for you.

Module	Use it when
`verdict4s`	You want a working client in one line. Brings its own transport.
`verdict4s-client`	You already have an http4s `Client[F]`, or want a specific backend.
`verdict4s-core`	You want the types and codecs only, with no effect system at all.

Each layer depends on the one below it, so taking verdict4s gives you all three. On the JVM they need Java 17 or later.

Mill

def mvnDeps = Seq(
  mvn"com.softinio::verdict4s::0.1.0"
)

sbt

libraryDependencies += "com.softinio" %%% "verdict4s" % "0.1.0"

The :: (Mill) and %%% (sbt) forms resolve the right artifact for whichever platform you are building, so the same line works for JVM and Scala.js.

Where to next

Getting started — your first request, on JVM and Scala.js
Typed questions — Ask, enum derivation, your own answer types
Errors and retries — what can fail, and what is retried
Bring your own client — any http4s backend, or an in-memory fake
No effect system — driving the protocol by hand
Other effect systems — ZIO, Future, and anything else
API reference — generated Scaladoc for each module

A note on dependencies

verdict4s-core depends on cats-core, circe and Iron. Iron is what carries the API's numeric and cardinality bounds in the types, and it is a public dependency: it appears in signatures such as Probability, so it comes along with the library.