Quoted pattern matching does not work when quote is in a val.

[smarter]

Compiler version

3.3.0-RC1-bin-20221215-ef653b6-NIGHTLY

Minimized code

After inlining, pat(3) is replaced by "ok" as expected in the following code:

import scala.quoted.*

inline def pat(inline e: Int): String = ${patImpl('e)}

private def patImpl(e: Expr[Int])(using Quotes): Expr[String] = {
  e match
    case '{ 3 } => '{"ok"}
    case _ => '{"other"}
}

def test = pat(3)

But if I put the quote in a pattern, then I get "other" instead:

private def patImpl(e: Expr[Int])(using Quotes): Expr[String] = {
  val Expr = '{ 3 }
  e match
    case Expr => '{"ok"}
    case _ => '{"other"}
}

Expectation

I think ideally both code snippets should behave the same. My usecase is that I'd like to check if some expression is already present in the input, and if not output what code should be generated (cf https://contributors.scala-lang.org/t/scala-3-macro-annotations-and-code-generation/6035), so I'd like to write the Expr once and use it both for pattern matching and as an output.

[hmf]

Related to #16533?

[nicolasstucki]

The limitation here is that the match becomes a e == Expr. Currently, the expression equality only checks if the trees are preferentially equal. We miss the context to be able to compare them semantically.

We provide the users with the matches to this operation

private def patImpl(e: Expr[Int])(using Quotes): Expr[String] = {
  val Expr = '{ 3 }
  if e.matches(Expr) then '{"ok"}
  else '{"other"}

Another way we could achieve it is to support splicing expressions into (as opposed to out of) a quoted pattern.

[smarter]

I see, thanks! Maybe we could warn on use of == on Expr to let the user know about .matches?