Generating Scala code trees from a Scala compiler plugin

Question

There are a few resources on the web that are instructive in writing Scala compiler plugins that pattern-match against the code, but these don't help in generating code (constructing symbol trees). Where should I start to figure out how to do this? (If there's an easier way than to manually build symbol trees, I'd be interested as well.)

For instance, I'd like write a plugin that replaces some code with a simple AST for this expression, where the variables (extracted from the original program code) could be of any type:

"" + hello + ", " + world + "!"

I realize this may be tricky because of boxing and toString, e.g. if hello were an object and world were an int, this should really be something like:

"".+(hello.toString().+(", ".+(new Integer(world).toString().+("!"))))

I don't know the answer to your question, but Miguel Garcia has put together the Scala Compiler Corner which is probably the best available compilation of resources about the Scala compiler. — Jorge Ortiz
– Jorge Ortiz, Commented Feb 12, 2010 at 4:55

retronym · Accepted Answer · 2010-02-12 06:23:03Z

3

If you generate the tree before the erasure compiler phase, you can type hello and world with Any, and call toString on them.

 ~: cat test.scala 
object test {
  def f(hello: Any, world: Any) = "" + hello + ", " + world + "!"
  f("1", "2")
  f(1, 1)
}
 ~: scalac -Xprint:typer test.scala 
[[syntax trees at end of typer]]// Scala source: test.scala
package <empty> {
  final object test extends java.lang.Object with ScalaObject {
    def this(): object test = {
      test.super.this();
      ()
    };
    def f(hello: Any, world: Any): java.lang.String = "".+(hello).+(", ").+(world).+("!");
    test.this.f("1", "2");
    test.this.f(1, 1)
  }
}

~: scalac -Xprint:erasure test.scala 
[[syntax trees at end of erasure]]// Scala source: test.scala
package <empty> {
  final class test extends java.lang.Object with ScalaObject {
    def this(): object test = {
      test.super.this();
      ()
    };
    def f(hello: java.lang.Object, world: java.lang.Object): java.lang.String = "".+(hello).+(", ").+(world).+("!");
    test.this.f("1", "2");
    test.this.f(scala.Int.box(1), scala.Int.box(1))
  }
}

answered Feb 12, 2010 at 6:23

retronym

55.1k12 gold badges158 silver badges168 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

xyzzyrz Over a year ago

Thanks for the reply, but this doesn't really tell me how to generate an AST.

BenjaminJackman · Accepted Answer · 2010-02-14 20:05:09Z

2

you might find something in this project: http://github.com/scala-incubator/autoproxy-plugin

answered Feb 14, 2010 at 20:05

BenjaminJackman

1,4391 gold badge10 silver badges18 bronze badges

1 Comment

xyzzyrz Over a year ago

Unfortunately, this plugin wasn't really instructive in how to construct ASTs.

Community · Accepted Answer · 2017-05-23 12:07:05Z

1

This thread looks relevant: Convert Scala AST to source code

Specifically, you can construct Scala AST with the TreeDSL mentioned. http://www.scala-lang.org/archives/downloads/distrib/files/nightly/docs/compiler/scala/tools/nsc/ast/TreeDSL.html

edited May 23, 2017 at 12:07

CommunityBot

11 silver badge

answered Sep 2, 2011 at 21:18

pdxleif

1,80016 silver badges15 bronze badges

1 Comment

pdxleif Over a year ago

Update: There's a project that expands on the TreeDSL and looks quite usable: github.com/eed3si9n/treehugger

Collectives™ on Stack Overflow

Generating Scala code trees from a Scala compiler plugin

3 Answers 3

1 Comment

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related