refactor: introduce decline to integrate command-line parsing with cats-effect

project.scala

@@ -9,7 +9,6 @@
 //> using dep org.typelevel::cats-effect::3.5.7
 //> using dep com.monovore::decline::2.5.0
 //> using dep com.monovore::decline-effect::2.5.0
-//> using dep com.github.scopt::scopt::4.1.0
 //> using test.dep org.scalatest::scalatest::3.2.19
 //> using dep org.typelevel::cats-effect-testing-scalatest::1.6.0
 

src/main/wacc/Main.scala

@@ -3,38 +3,38 @@ package wacc
 import scala.collection.mutable
 import cats.data.Chain
 import parsley.{Failure, Success}
-import scopt.OParser
 import java.io.File
 import java.io.PrintStream
 import cats.implicits.*
 
-import assemblyIR as asm
 import cats.effect.IO
-import cats.effect.IOApp
+import cats.effect.ExitCode
+
+import com.monovore.decline._
+import com.monovore.decline.effect._
+import com.monovore.decline.Argument
+
+import assemblyIR as asm
+
 
 case class CliConfig(
     file: File = new File(".")
 )
 
-val cliBuilder = OParser.builder[CliConfig]
-val cliParser = {
-  import cliBuilder._
-  OParser.sequence(
-    programName("wacc-compiler"),
-    help('h', "help")
-      .text("Prints this help message"),
-    arg[File]("<file>")
-      .text("Input WACC source file")
-      .required()
-      .action((f, c) => c.copy(file = f))
-      .validate(f =>
-        if (!f.exists) failure("File does not exist")
-        else if (!f.isFile) failure("File must be a regular file")
-        else if (!f.getName.endsWith(".wacc"))
-          failure("File must have .wacc extension")
-        else success
-      )
-  )
+given Argument[File] = Argument.from("file") { str =>
+  val file = File(str)
+  (
+    Option.when(file.exists())(file).toValidNel(s"File '${file.getAbsolutePath}' does not exist"),
+    Option
+      .when(file.isFile())(file)
+      .toValidNel(s"File '${file.getAbsolutePath}' must be a regular file"),
+    Option.when(file.getName.endsWith(".wacc"))(file).toValidNel("File must have .wacc extension")
+  ).mapN((_, _, _) => file)
+}
+
+val cliCommand: Command[File] =
+  Command("wacc-compiler", "Compile WACC programs") {
+    Opts.argument[File]("file")
   }
 
 def frontend(
@@ -87,13 +87,18 @@ def compile(filename: String, outFile: Option[File] = None)(using
     )
   } yield exitCode
 
-object Main extends IOApp.Simple {
-  override def run: IO[Unit] =
-    OParser.parse(cliParser, sys.env.getOrElse("WACC_ARGS", "").split(" "), CliConfig()).traverse_ {
-      config =>
+object Main
+    extends CommandIOApp(
+      name = "wacc-compiler",
+      header = "the ultimate wacc compiler",
+      version = "1.0"
+    ) {
+  def main: Opts[IO[ExitCode]] =
+    Opts.argument[File]("file").map { file =>
       compile(
-          config.file.getAbsolutePath,
-          outFile = Some(File(".", config.file.getName.stripSuffix(".wacc") + ".s"))
-        )
+        file.getAbsolutePath,
+        outFile = Some(File(".", file.getName.stripSuffix(".wacc") + ".s"))
+      ).map(ExitCode(_)) // turn the int into exit code for compatibility with commandioapp
+      // https://ben.kirw.in/decline/effect.html
     }
 }