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https://github.com/dmytromitin/dotty-patched
Eval library and patched Scala-3/Dotty compiler. Evaluating source code and trees at compile time hacking multi-staging programming
https://github.com/dmytromitin/dotty-patched
compilation compiler dotty eval evaluation macros metaprogramming runtime-compilation scala scala-3 scala3 scala3-metaprogramming
Last synced: 3 days ago
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Eval library and patched Scala-3/Dotty compiler. Evaluating source code and trees at compile time hacking multi-staging programming
- Host: GitHub
- URL: https://github.com/dmytromitin/dotty-patched
- Owner: DmytroMitin
- License: apache-2.0
- Created: 2022-10-28T18:35:37.000Z (about 2 years ago)
- Default Branch: main
- Last Pushed: 2022-11-02T02:26:40.000Z (about 2 years ago)
- Last Synced: 2024-01-29T04:41:42.066Z (11 months ago)
- Topics: compilation, compiler, dotty, eval, evaluation, macros, metaprogramming, runtime-compilation, scala, scala-3, scala3, scala3-metaprogramming
- Language: Scala
- Homepage:
- Size: 1.84 MB
- Stars: 19
- Watchers: 4
- Forks: 1
- Open Issues: 15
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# Dotty-patched and Eval
[](https://maven-badges.herokuapp.com/maven-central/com.github.dmytromitin/eval_3)
[](https://search.maven.org/search?q=g:%22com.github.dmytromitin%22%20AND%20a:%22eval_3%22)
[](https://oss.sonatype.org/content/groups/public/com/github/dmytromitin/eval_3/)
[](https://javadoc.io/doc/com.github.dmytromitin/eval_3)
[](https://index.scala-lang.org/dmytromitin/dotty-patched)
[](https://index.scala-lang.org/dmytromitin/dotty-patched/eval)
[](https://index.scala-lang.org/dmytromitin/dotty-patched/scala3-compiler-patched)
[](https://index.scala-lang.org/dmytromitin/dotty-patched/scala3-compiler-patched-assembly)
[](https://gitter.im/DmytroMitin/eval?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
[mvnrepository](https://mvnrepository.com/artifact/com.github.dmytromitin)
[repo1.maven](https://repo1.maven.org/maven2/com/github/dmytromitin/)
## Background
https://github.com/lampepfl/dotty
https://stackoverflow.com/questions/71390113/get-annotations-from-class-in-scala-3-macros
https://stackoverflow.com/questions/70945320/how-to-compile-and-execute-scala-code-at-run-time-in-scala3
https://github.com/DmytroMitin/dotty-patched/commit/fdf010ca4901b22961f3ae1cb3459b5fa194652e
## Dotty-patched and multi-staging in Scala 3 macros
`staging.run` [evaluates](https://docs.scala-lang.org/scala3/reference/metaprogramming/staging.html) a typed tree (wrapped into an `Expr`) into a value
(this seems similar to `context.eval`/`toolbox.eval` evaluating an untyped tree in [Scala 2](https://docs.scala-lang.org/overviews/reflection/symbols-trees-types.html#tree-creation-via-parse-on-toolboxes)).
This functionality exists in Scala 3/Dotty but is deliberately blocked in [macros](https://docs.scala-lang.org/scala3/reference/metaprogramming/macros.html)
(because of the [phase consistency principle](https://docs.scala-lang.org/scala3/reference/metaprogramming/macros.html#the-phase-consistency-principle)).
To unblock, a code expanding macros should be [compiled](https://www.scala-sbt.org/1.x/docs/Configuring-Scala.html#Configuring+Scala+tool+dependencies) with the compiler patched.
Macros themselves can be compiled with the standard compiler.
Staging dependency didn't have to be patched so far.
```scala
scalaVersion := "3.2.1" // 3.2.0, 3.1.3, ...
libraryDependencies += scalaOrganization.value %% "scala3-staging" % scalaVersion.value
// custom Scala settings
managedScalaInstance := false
ivyConfigurations += Configurations.ScalaTool
libraryDependencies ++= Seq(
scalaOrganization.value % "scala-library" % "2.13.10",
scalaOrganization.value %% "scala3-library" % "3.2.1",
"com.github.dmytromitin" %% "scala3-compiler-patched-assembly" % "3.2.1" % "scala-tool"
)
```
```scala
import scala.quoted.*
inline def printAtCompileTime[A](a: A): Unit = ${impl[A]('a)}
def impl[A: Type](a: Expr[A])(using Quotes): Expr[Unit] =
import quotes.reflect.*
given staging.Compiler = staging.Compiler.make(this.getClass.getClassLoader)
val aValue = staging.run(a) // evaluating a tree
println(aValue)
'{()}
```
```scala
sbt clean compile
```
```scala
printAtCompileTime(1 + 1) // 2 (at compile time)
```
## Eval
On contrary to `staging.run`, `Eval` evaluates into a value a source code rather than a tree. So it works on standard Scala 3.
```scala
scalaVersion := "3.2.1" // or 3.2.0
libraryDependencies += "com.github.dmytromitin" %% "eval" % "0.1"
```
```scala
sbt clean compile run
```
```scala
import com.github.dmytromitin.eval.Eval
Eval[Int]("1 + 1") // 2 (at runtime)
```
## Eval in Scala 3 macros
```scala
import com.github.dmytromitin.eval.Eval
import scala.quoted.*
inline def printAtCompileTime[A](a: A): Unit = ${impl[A]('a)}
def impl[A: Type](a: Expr[A])(using Quotes): Expr[Unit] =
import quotes.reflect.*
val str = a.asTerm.pos.sourceCode.getOrElse(
report.errorAndAbort(s"No source code for ${a.show}")
)
val aValue = Eval[A](str) // evaluating source code
println(aValue)
'{()}
```
```scala
sbt clean compile
```
```scala
printAtCompileTime(1 + 1) // 2 (at compile time)
```
## Some built-in Scala 3 macros
```scala
import com.github.dmytromitin.macros.eval.AnnotationsMacro.getAnnotations
import com.github.dmytromitin.macros.eval.PrintValueMacro.printAtCompileTime
printAtCompileTime(1 + 1)
//2
getAnnotations(classOf[scala.CanEqual[?, ?]])
//new scala.annotation.internal.SourceFile("library/src/scala/CanEqual.scala"), new scala.annotation.internal.Child[scala.CanEqual.derived.type](), new scala.annotation.implicitNotFound("Values of types ${L} and ${R} cannot be compared with == or !=")
```
```scala
// add custom Scala settings to build.sbt, see above
import com.github.dmytromitin.macros.run.AnnotationsMacro.getAnnotations
import com.github.dmytromitin.macros.run.PrintValueMacro.printAtCompileTime
printAtCompileTime(1 + 1)
//2
getAnnotations(classOf[scala.CanEqual[?, ?]])
//scala.List.apply[java.lang.String]("new scala.annotation.internal.SourceFile(\"library/src/scala/CanEqual.scala\")", "new scala.annotation.internal.Child[scala.CanEqual.derived.type]()", "new scala.annotation.implicitNotFound(\"Values of types ${L} and ${R} cannot be compared with == or !=\")")
```