Expand Code to Raw AST Scala 3 in the REPL

Question

I am currently doing a lot of compiler research. This not only entails to writing compiler plugins but also modifying the dotty compiler, from the parser to the typer. Therefore I need to constantly look at the raw ASTs to sketch the necessary transformations.

In Scala 2, the reflection library provided the following functionality:

   val expression = ....
   val tree = reify{expression}.tree
   showRaw(tree)

Now from what I understand from the docs, the final step has been replaced by Printer.TreeStructure.show(tree)

However, I can not find anything in the meta programming docs for an alternative to reify. Now I can obviously use various meta programming techniques inside a Scala program and print the tree to stdout but this is a very time consuming process compared to expanding in the REPL for a quick manual verification.

Is there a way to do this in the Scala 3 REPL?

Answer 1

You can define your own reify in your project

import scala.quoted.*

object App {
  inline def reify(inline a: Any) = ${reifyImpl('a)}

  def reifyImpl(a: Expr[Any])(using Quotes): Expr[String] = {
    import quotes.reflect.*
    Literal(StringConstant(Printer.TreeStructure.show(a.asTerm))).asExprOf[String]
  }
}

and use it in REPL

sbt console

scala> import App.reify

scala> reify{ class A }                                                                                                                                                             
val res0: String = Inlined(None, Nil, Block(List(ClassDef("A", DefDef("<init>", List(TermParamClause(Nil)), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), None, Nil)), Literal(UnitConstant())))

Unfortunately defining reify directly in REPL doesn't seem to work

scala> import scala.quoted.*; inline def reify(inline a: Any) = ${reifyImpl('a)}; def reifyImpl(a: Expr[Any])(using Quotes): Expr[String] = {import quotes.reflect.*; Literal(StringConstant(Printer.TreeStructure.show(a.asTerm))).asExprOf[String]}
def reify(a: Any): String
def reifyImpl
  (a: quoted.Expr[Any])(using x$2: quoted.Quotes): quoted.Expr[String]

scala> reify{class A}
-- Error:
1 |reify{class A}
  |^^^^^^^^^^^^^^
  |Failed to evaluate macro.
  |  Caused by class java.lang.ClassNotFoundException: rs$line$6
  |    java.lang.ClassLoader.loadClass(ClassLoader.java:418)
  |    java.lang.ClassLoader.loadClass(ClassLoader.java:351)
  |    dotty.tools.repl.AbstractFileClassLoader.loadClass(AbstractFileClassLoader.scala:55)
  |    dotty.tools.dotc.transform.Splicer$Interpreter.loadReplLineClass(Splicer.scala:402)
  |    dotty.tools.dotc.transform.Splicer$Interpreter.interpretedStaticMethodCall(Splicer.scala:354)
  |    dotty.tools.dotc.transform.Splicer$Interpreter.interpretTree(Splicer.scala:260)
  |    dotty.tools.dotc.transform.Splicer$Interpreter.interpretTree$$anonfun$2(Splicer.scala:281)
  |             
  | This location contains code that was inlined from rs$line$7:1

---

In 3.2.0 reify can be defined directly in REPL (scala-cli)

$ scala-cli

Welcome to Scala 3.2.0 (1.8.0_231, Java Java HotSpot(TM) 64-Bit GraalVM EE 19.3.0).
Type in expressions for evaluation. Or try :help.
                                                                                
scala> import scala.quoted.*; inline def reify(inline a: Any) = ${reifyImpl('a)}; def reifyImpl(a: Expr[Any])(using Quotes): Expr[String] = {import quotes.reflect.*; Literal(StringConstant(Printer.TreeStructure.show(a.asTerm))).asExprOf[String]}
def reify(a: Any): String
def reifyImpl
  (a: quoted.Expr[Any])(using x$2: quoted.Quotes): quoted.Expr[String]
                                                                                
scala> reify{class A}
val res0: String = Inlined(None, Nil, Block(List(ClassDef("A", DefDef("<init>", List(TermParamClause(Nil)), Inferred(), None), List(Apply(Select(New(Inferred()), "<init>"), Nil)), None, Nil)), Literal(UnitConstant())))