Base deskolemize on ApproximatingTypeMap

Author: odersky

src/dotty/tools/dotc/core/TypeOps.scala

@@ -122,100 +122,21 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
     def currentVariance = variance
   }
 
-  /** Approximate a type `tp` with a type that does not contain skolem types.
-   */
-  final def deskolemize(tp: Type): Type = deskolemize(tp, 1, Set())
-
-  private def deskolemize(tp: Type, variance: Int, seen: Set[SkolemType]): Type = {
-    def approx(lo: Type = defn.NothingType, hi: Type = defn.AnyType, newSeen: Set[SkolemType] = seen) =
-      if (variance == 0) NoType
-      else deskolemize(if (variance < 0) lo else hi, variance, newSeen)
-    tp match {
+  /** Approximate a type `tp` with a type that does not contain skolem types. */
+  object deskolemize extends ApproximatingTypeMap {
+    private var seen: Set[SkolemType] = Set()
+    def apply(tp: Type) = tp match {
       case tp: SkolemType =>
         if (seen contains tp) NoType
-        else approx(hi = tp.info, newSeen = seen + tp)
-      case tp: NamedType =>
-        val sym = tp.symbol
-        if (sym.isStatic) tp
         else {
-          val pre1 = deskolemize(tp.prefix, variance, seen)
-          if (pre1 eq tp.prefix) tp
-          else {
-            val d = tp.prefix.member(tp.name)
-            d.info match {
-              case TypeAlias(alias) => deskolemize(alias, variance, seen)
-              case _ =>
-                if (pre1.exists && !pre1.isRef(defn.NothingClass)) tp.derivedSelect(pre1)
-                else {
-                  ctx.log(s"deskolem: $tp: ${tp.info}")
-                  tp.info match {
-                    case TypeBounds(lo, hi) => approx(lo, hi)
-                    case info => NoType
-                  }
-                }
-            }
-          }
+          val saved = seen
+          seen += tp
+          try approx(hi = tp.info)
+          finally seen = saved
         }
-      case _: ThisType | _: BoundType | _: SuperType | NoType | NoPrefix =>
-        tp
-      case tp: RefinedType =>
-        val parent1 = deskolemize(tp.parent, variance, seen)
-        if (parent1.exists) {
-          val refinedInfo1 = deskolemize(tp.refinedInfo, variance, seen)
-          if (refinedInfo1.exists)
-            tp.derivedRefinedType(parent1, tp.refinedName, refinedInfo1)
-          else
-            approx(hi = parent1)
-        }
-        else approx()
-      case tp: TypeAlias =>
-        val alias1 = deskolemize(tp.alias, variance * tp.variance, seen)
-        if (alias1.exists) tp.derivedTypeAlias(alias1)
-        else approx(hi = TypeBounds.empty)
-      case tp: TypeBounds =>
-        val lo1 = deskolemize(tp.lo, -variance, seen)
-        val hi1 = deskolemize(tp.hi, variance, seen)
-        if (lo1.exists && hi1.exists) tp.derivedTypeBounds(lo1, hi1)
-        else approx(hi =
-          if (lo1.exists) TypeBounds.lower(lo1)
-          else if (hi1.exists) TypeBounds.upper(hi1)
-          else TypeBounds.empty)
-      case tp: ClassInfo =>
-        val pre1 = deskolemize(tp.prefix, variance, seen)
-        if (pre1.exists) tp.derivedClassInfo(pre1)
-        else NoType
-      case tp: AndOrType =>
-        val tp1d = deskolemize(tp.tp1, variance, seen)
-        val tp2d = deskolemize(tp.tp2, variance, seen)
-        if (tp1d.exists && tp2d.exists)
-          tp.derivedAndOrType(tp1d, tp2d)
-        else if (tp.isAnd)
-          approx(hi = tp1d & tp2d)  // if one of tp1d, tp2d exists, it is the result of tp1d & tp2d
-        else
-          approx(lo = tp1d & tp2d)
-      case tp: WildcardType =>
-        val bounds1 = deskolemize(tp.optBounds, variance, seen)
-        if (bounds1.exists) tp.derivedWildcardType(bounds1)
-        else WildcardType
       case _ =>
         if (tp.isInstanceOf[MethodicType]) assert(variance != 0, tp)
-        deskolemizeMap.mapOver(tp, variance, seen)
-    }
-  }
-
-  object deskolemizeMap extends TypeMap {
-    private var seen: Set[SkolemType] = _
-    def apply(tp: Type) = deskolemize(tp, variance, seen)
-    def mapOver(tp: Type, variance: Int, seen: Set[SkolemType]) = {
-      val savedVariance = this.variance
-      val savedSeen = this.seen
-      this.variance = variance
-      this.seen = seen
-      try super.mapOver(tp)
-      finally {
-        this.variance = savedVariance
-        this.seen = savedSeen
-      }
+        mapOver(tp)
     }
   }