2.10.0-M7でマクロを使うのにlibraryDependenciesの追加が必要だった

a.scala

import sbt._
import sbt.Keys._

object Scala210Build extends Build {

  lazy val scala210 = Project(
    id = "scala-210",
    base = file("."),
    settings = Project.defaultSettings ++ Seq(
      name := "Scala 210",
      organization := "org.example",
      version := "1.0",
      scalaVersion := "2.10.0-M7",
      // add other settings here
      libraryDependencies <+= scalaVersion { v => "org.scala-lang" % "scala-reflect" % v }
    )
  )
}

b.

package org.example

import scala.reflect.macros.Context
// import scala.reflect.makro.Context じゃなくて
import language.experimental.macros

import collection.mutable.ListBuffer
import collection.mutable.Stack