Merge pull request #7619 from dotty-staging/add-patmat-power-example

Add simple power test for patmat

Author: biboudis

tests/run-macros/quote-matcher-power.check

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+32.0
+512.0
+2.0
+1.0
+64.0

tests/run-macros/quote-matcher-power/Macro_1.scala

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+import scala.quoted._
+import scala.quoted.matching._
+
+object Macros {
+
+  def power_s(x: Expr[Double], n: Int)(given QuoteContext): Expr[Double] =
+    if (n == 0) '{1.0}
+    else if (n % 2 == 1) '{ $x * ${power_s(x, n - 1)} }
+    else '{ val y = $x * $x; ${power_s('y, n / 2)} }
+
+  inline def power(x: Double, inline n: Int): Double =
+    ${power_s('x, n)}
+
+  def power2(x: Double, y: Double): Double = if y == 0.0 then 1.0 else x * power2(x, y - 1.0)
+
+  inline def rewrite(expr: => Double): Double = ${rewrite('expr)}
+
+  // simple, 1-level, non-recursive rewriter for exponents
+  def rewrite(expr: Expr[Double])(given QuoteContext): Expr[Double] = {
+    val res = expr match {
+      // product rule
+      case '{ power2($a, $x) * power2($b, $y)} if a.matches(b) => '{ power2($a, $x + $y) }
+      // rules of 1
+      case '{ power2($a, 1)} => a
+      case '{ power2(1, $a)} => '{ 1.0 }
+      // rule of 0
+      case '{ power2($a, 0)} => '{ 1.0 }
+      // power rule
+      case '{ power2(power2($a, $x), $y)} => '{ power2($a, $x * $y ) }
+      case _ => expr
+    }
+    println(res.show)
+    res
+  }
+}

tests/run-macros/quote-matcher-power/Test_2.scala

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+import Macros._
+
+object Test {
+
+  def main(args: Array[String]): Unit = {
+    val x = 2
+    println(power(x, 5))
+
+    println(rewrite{ power2(2.0, 5.0) * power2(2.0, 4.0) })
+
+    println(rewrite{ power2(2.0, 1.0) })
+
+    println(rewrite{ power2(1.0, 1000) })
+
+    println(rewrite{ power2(power2(2.0, 2.0), 3.0) })
+  }
+}