Swam - Imports

When a module is instantiated, it is possible to import functions or values from Scala into the module. For instance, let’s assume we defined a function that prints its parameter on the console, and a simple WebAssembly module that imports and calls it.

import swam.text._
import swam.runtime._
import cats.effect._
import java.nio.file.Paths

implicit val cs = IO.contextShift(scala.concurrent.ExecutionContext.global)

def log(i: Int) = IO(println(s"got $i"))

val f =
  Blocker[IO].use { blocker =>
    for {
      engine <- Engine[IO](blocker)
      tcompiler <- Compiler[IO](blocker)
      mod <- engine.compile(tcompiler.stream(Paths.get("logged.wat"), true, blocker))
      inst <- mod.importing("console", "log" -> log _).instantiate
      f <- inst.exports.typed.function[Int, Int]("add42")
    } yield f
  }.unsafeRunSync()

running function f logs the parameter.

f(4).unsafeRunSync()
// got 4
// res0: Int = 46

It is also possible to use HLists to represent imported modules with several exposed fields. For instance, let’s import the console module with an extra colors field exposed.

import shapeless._

Blocker[IO].use { blocker =>
  for {
    engine <- Engine[IO](blocker)
    tcompiler <- Compiler[IO](blocker)
    mod <- engine.compile(tcompiler.stream(Paths.get("logged.wat"), true, blocker))
    inst <- mod.importing("console", "log" -> log _ :: "colors" -> 256 :: HNil).instantiate
    f <- inst.exports.typed.function[Int, Int]("add42")
  } yield f
}