How to pass arguments to a function of arbitrary number of parameters via macro?

Question

I have deconstructed Function, got it vparams, and now I am able to call:

  case class Action(f: Function, ts: List[TypeName]) {
    def render(ruleName: String): Expr[Unit] = c.Expr[Unit](q"""
      val p = ${c.prefix}
      val value1 = p.valueStack.pop().asInstanceOf[${ts(0)}]
      val value2 = p.valueStack.pop().asInstanceOf[${ts(1)}]
      p.valueStack.push($f(value1, value2))
    """)
  }

f is of arbitrary number of parameters that is known at compile time.

How to pass ts.count parameters from p.valueStack to a function f?

ghik · Accepted Answer · 2013-08-28 11:59:00Z

1

How about something like this:

case class Action(f: Function, ts: List[TypeName]) {
  def render(ruleName: String): Expr[Unit] = {
    val argNames = (1 to ts.size).map(i => newTermName(s"value$i"))
    val args = argNames.map(name => Ident(name))
    val valDefs = (ts zip argNames).map {
      case (tn, argName) =>
        q"val $argName = p.valueStack.pop().asInstanceOf[$tn]"
    }

    c.Expr[Unit]( q"""
      val p = ${c.prefix}
      ..$valDefs
      p.valueStack.push($f(..$args))
      """)
  }
}

This compiles (in Scala 2.10.2 with Macro Paradise plugin), but I didn't test whether it works.

answered Aug 28, 2013 at 11:59

ghik

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1 Comment

Alexander Myltsev Over a year ago

Eventually it does work. You can find the holy magic at parboiled2 wip branch

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