Use opaque types in matcher to abstract over Matchings

Author: nicolasstucki

library/src-3.x/scala/internal/quoted/Matcher.scala

@@ -32,6 +32,7 @@ object Matcher {
    */
   def unapply[Tup <: Tuple](scrutineeExpr: Expr[_])(implicit patternExpr: Expr[_], reflection: Reflection): Option[Tup] = {
     import reflection.{Bind => BindPattern, _}
+    import Matching._
 
     type Env = Set[(Symbol, Symbol)]
 
@@ -45,7 +46,7 @@ object Matcher {
      * @param `the[Env]` Set of tuples containing pairs of symbols (s, p) where s defines a symbol in `scrutinee` which corresponds to symbol p in `pattern`.
      * @return `None` if it did not match or `Some(tup: Tuple)` if it matched where `tup` contains the contents of the holes.
      */
-    def treeMatches(scrutinee: Tree, pattern: Tree) given Env: Option[Tuple] = {
+    def (scrutinee: Tree) =#= (pattern: Tree) given Env: Matching = {
 
       /** Check that both are `val` or both are `lazy val` or both are `var` **/
       def checkValFlags(): Boolean = {
@@ -56,7 +57,7 @@ object Matcher {
       }
 
       def bindingMatch(sym: Symbol) =
-        Some(Tuple1(new Bind(sym.name, sym)))
+        matched(new Bind(sym.name, sym))
 
       def hasBindTypeAnnotation(tpt: TypeTree): Boolean = tpt match {
         case Annotated(tpt2, Apply(Select(New(TypeIdent("patternBindHole")), "<init>"), Nil)) => true
@@ -67,9 +68,9 @@ object Matcher {
       def hasBindAnnotation(sym: Symbol) =
         sym.annots.exists { case Apply(Select(New(TypeIdent("patternBindHole")),"<init>"),List()) => true; case _ => true }
 
-      def treesMatch(scrutinees: List[Tree], patterns: List[Tree]): Option[Tuple] =
-        if (scrutinees.size != patterns.size) None
-        else foldMatchings(scrutinees.zip(patterns).map(treeMatches): _*)
+      def (scrutinees: List[Tree]) =##= (patterns: List[Tree]): Matching =
+        if (scrutinees.size != patterns.size) notMatched
+        else foldMatchings(scrutinees.zip(patterns).map((s, p) => s =#= p): _*)
 
       /** Normalieze the tree */
       def normalize(tree: Tree): Tree = tree match {
@@ -85,126 +86,129 @@ object Matcher {
             if patternHole.symbol == kernel.Definitions_InternalQuoted_patternHole &&
                s.tpe <:< tpt.tpe &&
                tpt2.tpe.derivesFrom(definitions.RepeatedParamClass) =>
-          Some(Tuple1(scrutinee.seal))
+          matched(scrutinee.seal)
 
         // Match a scala.internal.Quoted.patternHole and return the scrutinee tree
         case (IsTerm(scrutinee), TypeApply(patternHole, tpt :: Nil))
             if patternHole.symbol == kernel.Definitions_InternalQuoted_patternHole &&
                scrutinee.tpe <:< tpt.tpe =>
-          Some(Tuple1(scrutinee.seal))
+          matched(scrutinee.seal)
 
         //
         // Match two equivalent trees
         //
 
         case (Literal(constant1), Literal(constant2)) if constant1 == constant2 =>
-          Some(())
+          matched
 
         case (Typed(expr1, tpt1), Typed(expr2, tpt2)) =>
-          foldMatchings(treeMatches(expr1, expr2), treeMatches(tpt1, tpt2))
+          expr1 =#= expr2 && tpt1 =#= tpt2
 
         case (Ident(_), Ident(_)) if scrutinee.symbol == pattern.symbol || the[Env].apply((scrutinee.symbol, pattern.symbol)) =>
-          Some(())
+          matched
 
         case (Select(qual1, _), Select(qual2, _)) if scrutinee.symbol == pattern.symbol =>
-          treeMatches(qual1, qual2)
+          qual1 =#= qual2
 
         case (IsRef(_), IsRef(_)) if scrutinee.symbol == pattern.symbol =>
-          Some(())
+          matched
 
         case (Apply(fn1, args1), Apply(fn2, args2)) if fn1.symbol == fn2.symbol =>
-          foldMatchings(treeMatches(fn1, fn2), treesMatch(args1, args2))
+          fn1 =#= fn2 && args1 =##= args2
 
         case (TypeApply(fn1, args1), TypeApply(fn2, args2)) if fn1.symbol == fn2.symbol =>
-          foldMatchings(treeMatches(fn1, fn2), treesMatch(args1, args2))
+          fn1 =#= fn2 && args1 =##= args2
 
         case (Block(stats1, expr1), Block(stats2, expr2)) =>
-          foldMatchings(treesMatch(stats1, stats2), treeMatches(expr1, expr2))
+          // FIXME update the environment
+          stats1 =##= stats2 && expr1 =#= expr2
 
         case (If(cond1, thenp1, elsep1), If(cond2, thenp2, elsep2)) =>
-          foldMatchings(treeMatches(cond1, cond2), treeMatches(thenp1, thenp2), treeMatches(elsep1, elsep2))
+          cond1 =#= cond2 && thenp1 =#= thenp2 && elsep1 =#= elsep2
 
         case (Assign(lhs1, rhs1), Assign(lhs2, rhs2)) =>
           val lhsMatch =
-            if (treeMatches(lhs1, lhs2).isDefined) Some(())
-            else None
-          foldMatchings(lhsMatch, treeMatches(rhs1, rhs2))
+            if ((lhs1 =#= lhs2).isMatch) matched
+            else notMatched
+          lhsMatch && rhs1 =#= rhs2
 
         case (While(cond1, body1), While(cond2, body2)) =>
-          foldMatchings(treeMatches(cond1, cond2), treeMatches(body1, body2))
+          cond1 =#= cond2 && body1 =#= body2
 
         case (NamedArg(name1, expr1), NamedArg(name2, expr2)) if name1 == name2 =>
-          treeMatches(expr1, expr2)
+          expr1 =#= expr2
 
         case (New(tpt1), New(tpt2)) =>
-          treeMatches(tpt1, tpt2)
+          tpt1 =#= tpt2
 
         case (This(_), This(_)) if scrutinee.symbol == pattern.symbol =>
-          Some(())
+          matched
 
         case (Super(qual1, mix1), Super(qual2, mix2)) if mix1 == mix2 =>
-          treeMatches(qual1, qual2)
+          qual1 =#= qual2
 
         case (Repeated(elems1, _), Repeated(elems2, _)) if elems1.size == elems2.size =>
-          treesMatch(elems1, elems2)
+          elems1 =##= elems2
 
         case (IsTypeTree(scrutinee @ TypeIdent(_)), IsTypeTree(pattern @ TypeIdent(_))) if scrutinee.symbol == pattern.symbol =>
-          Some(())
+          matched
 
         case (IsInferred(scrutinee), IsInferred(pattern)) if scrutinee.tpe <:< pattern.tpe =>
-          Some(())
+          matched
 
         case (Applied(tycon1, args1), Applied(tycon2, args2)) =>
-          foldMatchings(treeMatches(tycon1, tycon2), treesMatch(args1, args2))
+          tycon1 =#= tycon2 && args1 =##= args2
 
         case (ValDef(_, tpt1, rhs1), ValDef(_, tpt2, rhs2)) if checkValFlags() =>
           val bindMatch =
             if (hasBindAnnotation(pattern.symbol) || hasBindTypeAnnotation(tpt2)) bindingMatch(scrutinee.symbol)
-            else Some(())
-          val returnTptMatch = treeMatches(tpt1, tpt2)
+            else matched
+          val returnTptMatch = tpt1 =#= tpt2
           val rhsEnv = the[Env] + (scrutinee.symbol -> pattern.symbol)
           val rhsMatchings = treeOptMatches(rhs1, rhs2) given rhsEnv
-          foldMatchings(bindMatch, returnTptMatch, rhsMatchings)
+          bindMatch && returnTptMatch && rhsMatchings
 
         case (DefDef(_, typeParams1, paramss1, tpt1, Some(rhs1)), DefDef(_, typeParams2, paramss2, tpt2, Some(rhs2))) =>
-          val typeParmasMatch = treesMatch(typeParams1, typeParams2)
+          val typeParmasMatch = typeParams1 =##= typeParams2
           val paramssMatch =
-            if (paramss1.size != paramss2.size) None
-            else foldMatchings(paramss1.zip(paramss2).map { (params1, params2) => treesMatch(params1, params2) }: _*)
+            if (paramss1.size != paramss2.size) notMatched
+            else foldMatchings(paramss1.zip(paramss2).map { (params1, params2) => params1 =##= params2 }: _*)
           val bindMatch =
             if (hasBindAnnotation(pattern.symbol)) bindingMatch(scrutinee.symbol)
-            else Some(())
-          val tptMatch = treeMatches(tpt1, tpt2)
+            else matched
+          val tptMatch = tpt1 =#= tpt2
           val rhsEnv =
             the[Env] + (scrutinee.symbol -> pattern.symbol) ++
               typeParams1.zip(typeParams2).map((tparam1, tparam2) => tparam1.symbol -> tparam2.symbol) ++
               paramss1.flatten.zip(paramss2.flatten).map((param1, param2) => param1.symbol -> param2.symbol)
-          val rhsMatch = treeMatches(rhs1, rhs2) given rhsEnv
+          val rhsMatch = (rhs1 =#= rhs2) given rhsEnv
 
-          foldMatchings(bindMatch, typeParmasMatch, paramssMatch, tptMatch, rhsMatch)
+          bindMatch && typeParmasMatch && paramssMatch && tptMatch && rhsMatch
 
         case (Lambda(_, tpt1), Lambda(_, tpt2)) =>
           // TODO match tpt1 with tpt2?
-          Some(())
+          matched
 
         case (Match(scru1, cases1), Match(scru2, cases2)) =>
-          val scrutineeMacth = treeMatches(scru1, scru2)
+          val scrutineeMacth = scru1 =#= scru2
           val casesMatch =
-            if (cases1.size != cases2.size) None
+            if (cases1.size != cases2.size) notMatched
             else foldMatchings(cases1.zip(cases2).map(caseMatches): _*)
-          foldMatchings(scrutineeMacth, casesMatch)
+          scrutineeMacth && casesMatch
 
         case (Try(body1, cases1, finalizer1), Try(body2, cases2, finalizer2)) =>
-          val bodyMacth = treeMatches(body1, body2)
+          val bodyMacth = body1 =#= body2
           val casesMatch =
-            if (cases1.size != cases2.size) None
+            if (cases1.size != cases2.size) notMatched
               else foldMatchings(cases1.zip(cases2).map(caseMatches): _*)
           val finalizerMatch = treeOptMatches(finalizer1, finalizer2)
-          foldMatchings(bodyMacth, casesMatch, finalizerMatch)
+          bodyMacth && casesMatch && finalizerMatch
 
         // Ignore type annotations
-        case (Annotated(tpt, _), _) => treeMatches(tpt, pattern)
-        case (_, Annotated(tpt, _)) => treeMatches(scrutinee, tpt)
+        case (Annotated(tpt, _), _) =>
+          tpt =#= pattern
+        case (_, Annotated(tpt, _)) =>
+          scrutinee =#= tpt
 
         // No Match
         case _ =>
@@ -225,26 +229,26 @@ object Matcher {
                  |
                  |
                  |""".stripMargin)
-          None
+          notMatched
       }
     }
 
-    def treeOptMatches(scrutinee: Option[Tree], pattern: Option[Tree]) given Env: Option[Tuple] = {
+    def treeOptMatches(scrutinee: Option[Tree], pattern: Option[Tree]) given Env: Matching = {
       (scrutinee, pattern) match {
-        case (Some(x), Some(y)) => treeMatches(x, y)
-        case (None, None) => Some(())
-        case _ => None
+        case (Some(x), Some(y)) => x =#= y
+        case (None, None) => matched
+        case _ => notMatched
       }
     }
 
-    def caseMatches(scrutinee: CaseDef, pattern: CaseDef) given Env: Option[Tuple] = {
-      val (caseEnv, patternMatch) = patternMatches(scrutinee.pattern, pattern.pattern)
+    def caseMatches(scrutinee: CaseDef, pattern: CaseDef) given Env: Matching = {
+      val (caseEnv, patternMatch) = scrutinee.pattern =%= pattern.pattern
 
       {
         implied for Env = caseEnv
         val guardMatch = treeOptMatches(scrutinee.guard, pattern.guard)
-        val rhsMatch = treeMatches(scrutinee.rhs, pattern.rhs)
-        foldMatchings(patternMatch, guardMatch, rhsMatch)
+        val rhsMatch = scrutinee.rhs =#= pattern.rhs
+        patternMatch && guardMatch && rhsMatch
       }
     }
 
@@ -258,34 +262,34 @@ object Matcher {
      * @return The new environment containing the bindings defined in this pattern tuppled with
      *         `None` if it did not match or `Some(tup: Tuple)` if it matched where `tup` contains the contents of the holes.
      */
-    def patternMatches(scrutinee: Pattern, pattern: Pattern) given Env: (Env, Option[Tuple]) = (scrutinee, pattern) match {
+    def (scrutinee: Pattern) =%= (pattern: Pattern) given Env: (Env, Matching) = (scrutinee, pattern) match {
       case (Pattern.Value(v1), Pattern.Unapply(TypeApply(Select(patternHole @ Ident("patternHole"), "unapply"), List(tpt)), Nil, Nil))
           if patternHole.symbol.owner.fullName == "scala.runtime.quoted.Matcher$" =>
-        (the[Env], Some(Tuple1(v1.seal)))
+        (the[Env], matched(v1.seal))
 
       case (Pattern.Value(v1), Pattern.Value(v2)) =>
-        (the[Env], treeMatches(v1, v2))
+        (the[Env], v1 =#= v2)
 
       case (Pattern.Bind(name1, body1), Pattern.Bind(name2, body2)) =>
         val bindEnv = the[Env] + (scrutinee.symbol -> pattern.symbol)
-        patternMatches(body1, body2) given bindEnv
+        (body1 =%= body2) given bindEnv
 
       case (Pattern.Unapply(fun1, implicits1, patterns1), Pattern.Unapply(fun2, implicits2, patterns2)) =>
-        val funMatch = treeMatches(fun1, fun2)
+        val funMatch = fun1 =#= fun2
         val implicitsMatch =
-          if (implicits1.size != implicits2.size) None
-          else foldMatchings(implicits1.zip(implicits2).map(treeMatches): _*)
+          if (implicits1.size != implicits2.size) notMatched
+          else foldMatchings(implicits1.zip(implicits2).map((i1, i2) => i1 =#= i2): _*)
         val (patEnv, patternsMatch) = foldPatterns(patterns1, patterns2)
-        (patEnv, foldMatchings(funMatch, implicitsMatch, patternsMatch))
+        (patEnv, funMatch && implicitsMatch && patternsMatch)
 
       case (Pattern.Alternatives(patterns1), Pattern.Alternatives(patterns2)) =>
         foldPatterns(patterns1, patterns2)
 
       case (Pattern.TypeTest(tpt1), Pattern.TypeTest(tpt2)) =>
-        (the[Env], treeMatches(tpt1, tpt2))
+        (the[Env], tpt1 =#= tpt2)
 
       case (Pattern.WildcardPattern(), Pattern.WildcardPattern()) =>
-        (the[Env], Some(()))
+        (the[Env], matched)
 
       case _ =>
         if (debug)
@@ -305,30 +309,56 @@ object Matcher {
                |
                |
                |""".stripMargin)
-        (the[Env], None)
+        (the[Env], notMatched)
     }
 
-    def foldPatterns(patterns1: List[Pattern], patterns2: List[Pattern]) given Env: (Env, Option[Tuple]) = {
-      if (patterns1.size != patterns2.size) (the[Env], None)
-      else patterns1.zip(patterns2).foldLeft((the[Env], Option[Tuple](()))) { (acc, x) =>
-        val (env, res) = patternMatches(x._1, x._2) given acc._1
-        (env, foldMatchings(acc._2, res))
+    def foldPatterns(patterns1: List[Pattern], patterns2: List[Pattern]) given Env: (Env, Matching) = {
+      if (patterns1.size != patterns2.size) (the[Env], notMatched)
+      else patterns1.zip(patterns2).foldLeft((the[Env], matched)) { (acc, x) =>
+        val (env, res) = (x._1 =%= x._2) given acc._1
+        (env, acc._2 && res)
       }
     }
 
     implied for Env = Set.empty
-    treeMatches(scrutineeExpr.unseal, patternExpr.unseal).asInstanceOf[Option[Tup]]
+    (scrutineeExpr.unseal =#= patternExpr.unseal).asOptionOfTuple.asInstanceOf[Option[Tup]]
   }
 
-  /** Joins the mattchings into a single matching. If any matching is `None` the result is `None`.
-   *  Otherwise the result is `Some` of the concatenation of the tupples.
-   */
-  private def foldMatchings(matchings: Option[Tuple]*): Option[Tuple] = {
-    // TODO improve performance
-    matchings.foldLeft[Option[Tuple]](Some(())) {
-      case (Some(acc), Some(holes)) => Some(acc ++ holes)
-      case (_, _) => None
+  /** Result of matching a part of an expression */
+  private opaque type Matching = Option[Tuple]
+
+  private object Matching {
+
+    def notMatched: Matching = None
+    val matched: Matching = Some(())
+    def matched(x: Any): Matching = Some(Tuple1(x))
+
+    def (self: Matching) asOptionOfTuple: Option[Tuple] = self
+
+    /** Concatenates the contents of two sucessful matchings or return a `notMatched` */
+    def (self: Matching) && (that: Matching): Matching = self match {
+      case Some(x) =>
+        that match {
+          case Some(y) => Some(x ++ y)
+          case _ => None
+        }
+      case _ => None
     }
+
+    /** Is this matching the result of a successful match */
+    def (self: Matching) isMatch: Boolean = self.isDefined
+
+    /** Joins the mattchings into a single matching. If any matching is `None` the result is `None`.
+     *  Otherwise the result is `Some` of the concatenation of the tupples.
+     */
+    def foldMatchings(matchings: Matching*): Matching = {
+      // TODO improve performance
+      matchings.foldLeft[Matching](Some(())) {
+        case (Some(acc), Some(holes)) => Some(acc ++ holes)
+        case (_, _) => None
+      }
+    }
+
   }
 
 }