Kotlin with extern

Import kotlin from the same jvm plugin that provides Java. The signature uses Zolo types and the body uses Kotlin. Call the result like any other Zolo function. These programs run with the CLI and an installed JVM plugin.

// parity-timeout-ms:300000

use plugin jvm::{kotlin}

extern kotlin fn greet(name: str) -> str {
    return "Olá, $name!"
}

extern kotlin fn exact(value: int) -> int {
    return value
}

extern kotlin fn relay(callback: fn(int) -> int) -> int {
    return callback(41L)
}

extern kotlin async fn later(value: int) -> int {
    import kotlin.coroutines.suspendCoroutine
    import kotlin.coroutines.resume
    return suspendCoroutine { continuation ->
        Thread { continuation.resume(value + 1L) }.start()
    }
}

let value = 40
let answer: int = extern kotlin { value + 2L }
print(greet("Kotlin"))
print(exact(9007199254740993))
print(relay(|number| number + 1))
print(answer)
print(await later(41))

// expected:

// Olá, Kotlin!

// 9007199254740993

// 42

// 42

// 42

int maps to Kotlin Long; use i32 for Kotlin Int. str maps to String, nullable values to nullable native types, arrays to typed collections and callbacks to Kotlin function types. For a standalone capture, specify the expected result: let answer: int = extern kotlin { value + 2L }.

Sources and objects

use plugin jvm::{kotlin as k}

extern k from "./kotlin_fixtures/Person.kt" use {Person}

extern k fn same(person: Person) -> Person {
    return person
}

let person = Person.new(name: "João", age: 30)
print(person.name)
person.age = 31
print(person.age)
print(person.greeting())
print(person == same(person))

// expected:
// João
// 31
// Olá, João!
// true

extern kotlin from "./Person.kt" use {Person} follows the importing Zolo file. Supported public classes expose constructors, methods and mutable properties. Live objects retain their native identity and state across prepared bindings. Reachable sibling Kotlin sources are compiled together.

extern kotlin async fn creates a real suspend function and returns a Zolo Future. Imported suspend APIs and Java CompletionStage results use the same async boundary. Kotlin callbacks return to the owning Zolo runtime and may make nested foreign calls. Cancellation requests interruption or cancellation of the adapted operation; work that ignores it can continue.

Maven and setup

// Prepare with `zolo install` or `zolo run ... --install=auto`.
use plugin jvm::{kotlin}

extern kotlin deps {
    "com.google.guava:guava" = "33.4.0-jre"
}

extern kotlin fn join(values: [str]) -> str {
    import com.google.common.base.Joiner
    return Joiner.on(", ").join(values.asIterable())
}

print(join(["Kotlin", "Maven", "Zolo"]))

// expected:
// Kotlin, Maven, Zolo

Kotlin and Java share extern ... deps and [foreign.jvm.dependencies] declarations. Prepare with zolo install main.zolo, or permit first-run preparation with --install=auto. Projects default to manual installation. --offline --frozen consumes the prepared, locked closure.

Source preparation and native editor queries need a Java8+ JDK and the pinned Kotlin compiler/tooling closure. From a repository checkout, acquire it explicitly:

python plugins/jvm/tools/install-kotlin.py --destination .zolo-tools/kotlin-2.3.20

Set the printed ZOLO_KOTLIN_HOME and ZOLO_KOTLIN_ANALYSIS_HOME paths; ZOLO_JAVA_HOME selects Java. Acquisition verifies pinned SHA256 hashes and does not change a global Kotlin installation. Opening the editor does not download dependencies or execute authored code.

Compiler and analysis helpers produce diagnostics/bytecode in isolated temporary workspaces; invocation runs through JNI inside the Zolo process. Editor features use Kotlin's native Analysis API over current unsaved text, including supported autoimport edits.

Artifacts retain compiled classes, Kotlin stdlib, dependencies and source snapshots. VM, native and LLVM support dynamic/embed/static plugin packaging without original sources or the Kotlin compiler. Deployment still needs a compatible JRE. The default target is Java8; newer APIs and libraries may require a newer runtime. Hosted wasm-aot execution is unavailable. Acceptance currently covers Windows x64; other platforms need independent validation.