Merge pull request #11817 from rjolly/try

Add try method in safe throws strawman

Author: nicolasstucki

tests/run/safeThrowsStrawman2.check

@@ -0,0 +1,3 @@
+1
+failed
+failed

tests/run/safeThrowsStrawman2.scala

@@ -0,0 +1,47 @@
+import language.experimental.erasedDefinitions
+
+object scalax:
+  erased class CanThrow[-E <: Exception]
+
+  infix type throws[R, +E <: Exception] = CanThrow[E] ?=> R
+
+  class Fail extends Exception
+
+  def raise[E <: Exception](e: E): Nothing throws E = throw e
+
+  private class Result[T]:
+    var value: T = scala.compiletime.uninitialized
+
+  def try1[R, E <: Exception](body: => R throws E): (E => Unit) => R = { c =>
+    val res = new Result[R]
+    try
+      given CanThrow[E] = ???
+      res.value = body
+    catch c.asInstanceOf[Throwable => Unit]
+    res.value
+  }
+
+  extension [R, E <: Exception](t: (E => Unit) => R) def catch1(c: E => Unit) = t(c)
+
+import scalax._
+
+def foo(x: Boolean): Int throws Fail =
+  if x then 1 else raise(Fail())
+
+def bar(x: Boolean)(using CanThrow[Fail]): Int = foo(x)
+def baz: Int throws Exception = foo(false)
+
+@main def Test =
+  try1 {
+    println(foo(true))
+    println(foo(false))
+  } catch1 {
+    case ex: Fail =>
+      println("failed")
+  }
+  try1 {
+    println(baz)
+  } catch1 {
+    case ex: Fail =>
+      println("failed")
+  }