Gestalt

An experiment and tutorial on how to create a solid and portable macros system based on solid methodology and principles.

Design Goals:

• Portable -- better IDE experience, works both in Scala and Dotty
• Solid -- friendly typing error instead of compiler crashes or hacks
• Friendly -- no knowledge about compiler internals, no dependent universes

Examples

import scala.gestalt._

object Test {
  def plus(a: Int, b: Int): Int = meta {
    q"$a + $b"
  }
}

Design

• Only blackbox macros
• Separation of typed and untyped trees
• Only inspection of typed trees
• Only semantic information for typed trees

Philosophy

The design space of a macro system is large. Gestalt aims to be simple, solid and portable for the 80% common use cases.

a ) Assumptions on compiler implementation

• more assumptions
• fewer assumptions (✓) : portability & easy implementation

b ) Assumptions on macro usage

• more assumptions (✓) : focus on 80% common cases, make them easy
• fewer assumptions

c) Features

• more features
• fewer features (✓) : metaprogramming is hard, restrict power, implementation solid

Test

• sbt macros/test:run

Paper

Gestalt : The Road for Lightweight Portable Macros