Add quoted.Expr of contextual function beta-reduction

library/src-2.x/scala/quoted/Expr.scala

@@ -0,0 +1,49 @@
+package scala.quoted
+
+import scala.runtime.quoted.Unpickler.Pickled
+
+sealed abstract class Expr[+T] {
+
+  /** Evaluate the contents of this expression and return the result.
+   *
+   *  May throw a FreeVariableError on expressions that came from a macro.
+   */
+  final def run(implicit toolbox: Toolbox): T = toolbox.run(this)
+
+}
+
+/** All implementations of Expr[T].
+ *  These should never be used directly.
+ */
+object Exprs {
+  /** An Expr backed by a pickled TASTY tree */
+  final class TastyExpr[+T](val tasty: Pickled, val args: Seq[Any]) extends Expr[T] {
+    override def toString: String = s"Expr(<pickled tasty>)"
+  }
+
+  /** An Expr backed by a lifted value.
+   *  Values can only be of type Boolean, Byte, Short, Char, Int, Long, Float, Double, Unit, String or Null.
+   */
+  final class LiftedExpr[+T](val value: T) extends Expr[T] {
+    override def toString: String = s"Expr($value)"
+  }
+
+  /** An Expr backed by a tree. Only the current compiler trees are allowed.
+   *
+   *  These expressions are used for arguments of macros. They contain and actual tree
+   *  from the program that is being expanded by the macro.
+   *
+   *  May contain references to code defined outside this TastyTreeExpr instance.
+   */
+  final class TastyTreeExpr[Tree](val tree: Tree) extends quoted.Expr[Any] {
+    override def toString: String = s"Expr(<tasty tree>)"
+  }
+
+  // TODO Use a List in FunctionAppliedTo(val f: Expr[_], val args: List[Expr[_]])
+  // FIXME: Having the List in the code above trigers an assertion error while testing dotty.tools.dotc.reporting.ErrorMessagesTests.i3187
+  //        This test does redefine `scala.collection`. Further investigation is needed.
+  /** An Expr representing `'{($f).apply($x1, ..., $xn)}` but it is beta-reduced when the closure is known */
+  final class FunctionAppliedTo[+R](val f: Expr[_], val args: Array[Expr[_]]) extends Expr[R] {
+    override def toString: String = s"Expr($f <applied to> ${args.toList})"
+  }
+}