Can't use q"<foo></foo>" to match the passing tree

[freewind]

For the code:

Macros.manipulate(<foo></foo>)

If I define the manipulate as:

object Macros {
  def manipulate(elem: Elem): Elem = macro Bundle.impl
}

class Bundle(val c: Context) extends MacroLiftables {
  import c.universe._
  def impl(elem: Tree): Tree = {
    val q"<foo></foo>" = elem
    q"$result"
  }
}

It can never match:

[error] /Users/twer/workspace/xml-example/core/src/main/scala/Test.scala:17: exception during macro expansion:
[error] scala.MatchError: {
[error]   {
[error]     new scala.xml.Elem(null, "foo", scala.xml.Null, scala.this.xml.TopScope, false)
[error]   }
[error] } (of class scala.reflect.internal.Trees$Block)
[error]     at Bundle.impl(Macros.scala:17)
[error]   println(Macros.manipulate(<foo></foo>))
[error]                            ^
[error] one error found
[error] (core/compile:compile) Compilation failed
[error] Total time: 2 s, completed Mar 7, 2015 8:40:54 PM
>

[freewind]

Some investigation:

    def info(s: String) = {
      c.info(c.enclosingPosition, s, force = true)
    }

    info(
      s"""
        |============================
        |passing elem:
        |${showCode(elem)}
        |--------------------------
        |${showCode(q"<foo></foo>")}
        |============================
      """.stripMargin)

Will print:

[info] ============================
[info] passing elem:
[info] {
[info]   {
[info]     new scala.xml.Elem(null, "foo", scala.xml.Null, scala.xml.$scope, false)
[info]   }
[info] }
[info] --------------------------
[info] new _root_.scala.xml.Elem(null, "foo", _root_.scala.xml.Null, scala.xml.TopScope, false)
[info] ============================

[densh]

Hi @freewind, please see this stackoverflow answer.

[freewind]

Seems I need to write:

val q"${result: scala.xml.Elem}" = elem
val q"<foo></foo>" = q"$result"

It can match this time, is it expected usage?

[freewind]

Thanks, just noticed you reply, I will see that answer