Mirror of forum.nim-lang.org

10406 :: [Scala background] How does a macro in Scala differs from macro in Nim?

• hamidrb80 (orginal) [2023-08-14T14:30:34+02:00] view original

  Hey! I hope you have a good time.

  recently I've noticed that Scala has Macros with the ability to manipulate AST just like Nim.

  but surprisingly they don't advertising it ( I can't see much tutorials/projects about it ) which is opposite in Nim.

  If you have background in programming with Scala, could you please explain how does a macro in Scala and Nim differ AND why aren't they more popular in Scala?

  thanks

---

• Araq (orginal) [2023-08-14T18:53:36+02:00] view original

  Macros have been added later in Scala's history, when much of the rest of the Scala was already designed and Scala is a much more complex language than Nim so they had bad experiences with them and so they are not promoting them and iiirc Scala 3 lacks them entirely.

---

• termer (orginal) [2023-08-14T19:33:12+02:00] view original

  Scala 3 sucks lol, did you see what they did the the syntax?

---

• bpr (orginal) [2023-08-14T22:42:33+02:00] view original

  iirc Scala 3 lacks them entirely.

  https://docs.scala-lang.org/scala3/guides/macros/macros.html https://eed3si9n.com/intro-to-scala-3-macros/

---

• Araq (orginal) [2023-08-14T22:55:21+02:00] view original

  So they did add them again. Interesting, I remember Odersky saying that he considers to leave them out.

  I stand corrected.

---

• radekm (orginal) [2023-08-14T23:28:56+02:00] view original

  I believe (not sure) that in Nim macros run before typechecking so you can't get typed AST?

---

• elcritch (orginal) [2023-08-14T23:38:26+02:00] view original

  You can do both:

  macro foo(ast: untyped) = ...
  macro foo(ast: typed) = ...
  Run

---

• awr1 (orginal) [2023-08-15T00:01:42+02:00] view original

  If you have background in programming with Scala, could you please explain how does a macro in Scala and Nim differ AND why aren't they more popular in Scala?

  I suspect it may be because the language is in a "Python 2 -> 3" bifurcation moment.

  It has been a long time since I've personally programmed Scala, so doing a cursory glance (also take this with a grain of salt):

  • Scala's AST macros seem to be strong enough for build-time binding construction. This is common for languages that get to have a bit more of a robust macro system (even Rust, with its weaker token tree model) but one of the advantages of using, e.g. Futhark or Nimterop is that, while these utilities shell-out to CLI tools much like those other utilities, they are more unique in that their Nim counterparts execute within Nim itself and not through a build-system because Nim allows for certain degrees of system interaction at compiletime - i.e. `staticExec` and the CTFE FFI.
  • Scala seems to have a serialized AST/IR format and a visualization tool for that format. I assume this serves a similar purpose as MIR does in Rust.
  • The API seems to be a little stricter up front in Scala's, e.g. Nim's macro API takes in NimNode frequently, but Scala's is more specific, quotes.reflect.Term, etc.
  • The thing that confuses me the most is the statement that Scala's macros are expanded after all typechecking. One of Nim's key adds here is that it gives you the option for macro input in a lispier, DSL-focused way via untyped, or by typed if one prefers the input to semchecked prior to expansion for better errors. At one point it seems like Scala 2 had something like this but it seems to have been eliminated as it exposed certain compiler internals. (Nim, by contrast, embraces this fact, although there is something of a break between NimNode, the macro AST, and the PNode API that exists internally to the compiler).
  • There are conflicting resources between Scala 2 and Scala 3 but the above suggests APIs like sameType, typeof, etc. are not available in Scala the same way they would be in Nim.
  • Nim intentionally bisects the macro API into templates and the more powerful (and dangerous?) AST macros. An argument can be made that the latter is essentially a cleaner quasiquote.

---

• Araq (orginal) [2023-08-15T00:18:56+02:00] view original

  Actually I want Nim to move away from untyped to typed macros, or rather to semityped but it's probably a decade away.

---

• namisboss (orginal) [2023-08-15T03:20:14+02:00] view original

  This is the first time I've seen semityped. What is it?

---

• awr1 (orginal) [2023-08-15T03:47:36+02:00] view original

  I assume a reference to this

---

• hamidrb80 (orginal) [2023-08-15T12:19:24+02:00] view original

  beef has micros

---