project.scala

@@ -13,6 +13,8 @@
 //> using dep org.slf4j:slf4j-simple:2.0.17
 //> using test.dep org.scalatest::scalatest::3.2.19
 //> using dep org.typelevel::cats-effect-testing-scalatest::1.6.0
+//> using dep "co.fs2::fs2-core:3.11.0"
+//> using dep co.fs2::fs2-io:3.11.0
 
 // sensible defaults for warnings and compiler checks
 //> using options -deprecation -unchecked -feature

src/main/wacc/Main.scala

@@ -15,6 +15,8 @@ import com.monovore.decline.effect._
 import org.typelevel.log4cats.slf4j.Slf4jLogger
 import org.typelevel.log4cats.Logger
 
+import fs2.Stream
+
 import assemblyIR as asm
 import cats.data.ValidatedNel
 import java.io.File
@@ -147,8 +149,13 @@ def compileCommandParallel(
     log: Boolean,
     outDir: Option[Path]
 ): IO[ExitCode] =
-  files
-    .parTraverse { file => compile(file.toAbsolutePath, outDir, log) }
+  Stream
+    .emits(files.toList)
+    .parEvalMapUnordered(Runtime.getRuntime.availableProcessors()) { file =>
+      compile(file.toAbsolutePath, outDir, log)
+    }
+    .compile
+    .toList
     .map { exitCodes =>
       exitCodes.filter(_ != 0) match {
         case Nil        => ExitCode.Success