Change/higher kinded

src/dotty/tools/dotc/config/Config.scala

@@ -27,7 +27,7 @@ object Config {
   /** Show subtype traces for all deep subtype recursions */
   final val traceDeepSubTypeRecursions = false
 
-  final val verboseExplainSubtype = true
+  final val verboseExplainSubtype = false
 
   /** When set, use new signature-based matching.
    *  Advantantage of doing so: It's supposed to be faster
@@ -43,4 +43,9 @@ object Config {
    *  for large constraints.
    */
   final val trackConstrDeps = true
+
+  /** Check that variances of lambda arguments match the
+   *  variance of the underlying lambda class.
+   */
+  final val checkLambdaVariance = false
 }

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

@@ -33,8 +33,11 @@ class Definitions {
   private def newTopClassSymbol(name: TypeName, flags: FlagSet, parents: List[TypeRef]) =
     completeClass(newCompleteClassSymbol(ScalaPackageClass, name, flags, parents))
 
+  private def newTypeField(cls: ClassSymbol, name: TypeName, flags: FlagSet, scope: MutableScope) =
+    scope.enter(newSymbol(cls, name, flags, TypeBounds.empty))
+
   private def newTypeParam(cls: ClassSymbol, name: TypeName, flags: FlagSet, scope: MutableScope) =
-    scope.enter(newSymbol(cls, name, flags | TypeParamCreationFlags, TypeBounds.empty))
+    newTypeField(cls, name, flags | TypeParamCreationFlags, scope)
 
   private def newSyntheticTypeParam(cls: ClassSymbol, scope: MutableScope, paramFlags: FlagSet, suffix: String = "T0") =
     newTypeParam(cls, suffix.toTypeName.expandedName(cls), ExpandedName | paramFlags, scope)
@@ -421,59 +424,69 @@ class Definitions {
 
   def functionArity(tp: Type) = tp.dealias.argInfos.length - 1
 
-  // ----- Higher kinds machinery ------------------------------------------
+  // ----- LambdaXYZ traits ------------------------------------------
 
-  private var _hkTraits: Set[Symbol] = Set()
+  private var myLambdaTraits: Set[Symbol] = Set()
 
   /** The set of HigherKindedXYZ traits encountered so far */
-  def hkTraits: Set[Symbol] = _hkTraits
+  def lambdaTraits: Set[Symbol] = myLambdaTraits
 
-  private var hkTraitOfArity = mutable.Map[List[Int], ClassSymbol]()
+  private var lambdaTraitForVariances = mutable.Map[List[Int], ClassSymbol]()
 
   /** The HigherKinded trait corresponding to symbols `boundSyms` (which are assumed
    *  to be the type parameters of a higher-kided type). This is a class symbol that
    *  would be generated by the following schema.
    *
-   *      class HigherKindedXYZ { type v_n _$hk$0; ...; type v_n _$Hk$n }
+   *      class LambdaXYZ extends Object with P1 with ... with Pn {
+   *        type v_1 $hk$Arg0; ...; type v_N $hk$ArgN;
+   *        type Apply
+   *      }
    *
    *  Here:
    *
-   *   - XYZ is a string with one letter for each variant of a bound symbols,
-   *     using `P` (positive variance), `N` (negative variance), `I` (invariant).
    *   - v_i are the variances of the bound symbols (i.e. +, -, or empty).
-   *   - _$hk$i are higher-kinded parameter names, which are specially treated in type application.
+   *   - XYZ is a string of length N with one letter for each variant of a bound symbol,
+   *     using `P` (positive variance), `N` (negative variance), `I` (invariant).
+   *   - for each positive or negative variance v_i there is a parent trait Pj which
+   *     is the same as LambdaXYZ except that it has `I` in i-th position.
    */
-  def hkTrait(vcs: List[Int]) = {
+  def lambdaTrait(vcs: List[Int]): ClassSymbol = {
+    assert(vcs.nonEmpty)
 
     def varianceFlags(v: Int) = v match {
       case -1 => Contravariant
-      case  0 => Covariant
-      case  1 => EmptyFlags
+      case  0 => EmptyFlags
+      case  1 => Covariant
     }
 
     val completer = new LazyType  {
       def complete(denot: SymDenotation)(implicit ctx: Context): Unit = {
         val cls = denot.asClass.classSymbol
         val paramDecls = newScope
         for (i <- 0 until vcs.length)
-          newTypeParam(cls, tpnme.higherKindedParamName(i), EmptyFlags, paramDecls)
-        denot.info = ClassInfo(ScalaPackageClass.thisType, cls, List(ObjectClass.typeRef), paramDecls)
+          newTypeParam(cls, tpnme.lambdaArgName(i), varianceFlags(vcs(i)), paramDecls)
+        newTypeField(cls, tpnme.Apply, Covariant, paramDecls)
+        val parentTraitRefs =
+          for (i <- 0 until vcs.length if vcs(i) != 0)
+          yield lambdaTrait(vcs.updated(i, 0)).typeRef
+        denot.info = ClassInfo(
+            ScalaPackageClass.thisType, cls, ObjectClass.typeRef :: parentTraitRefs.toList, paramDecls)
       }
     }
 
-    val traitName = tpnme.higherKindedTraitName(vcs)
+    val traitName = tpnme.lambdaTraitName(vcs)
 
     def createTrait = {
       val cls = newClassSymbol(
         ScalaPackageClass,
         traitName,
         Trait | Interface | Synthetic,
         completer)
-      _hkTraits += cls
+      myLambdaTraits += cls
       cls
     }
 
-    hkTraitOfArity.getOrElseUpdate(vcs, createTrait)
+    lambdaTraitForVariances.getOrElseUpdate(vcs, createTrait)
   }
 
   // ----- primitive value class machinery ------------------------------------------

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

@@ -378,7 +378,7 @@ object Denotations {
         case info: SignedType =>
           try info.signature
           catch { // !!! DEBUG
-            case ex: MatchError =>
+            case ex: Throwable =>
               println(s"cannot take signature of ${info.show}")
               throw ex
           }

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

@@ -198,8 +198,9 @@ object Flags {
   final val Final = commonFlag(6, "final")
 
   /** A method symbol. */
-  final val MethodCommon = commonFlag(7, "<method>")
-  final val Method = MethodCommon.toTermFlags
+  final val MethodOrHKCommon = commonFlag(7, "<method>")
+  final val Method = MethodOrHKCommon.toTermFlags
+  final val HigherKinded = MethodOrHKCommon.toTypeFlags
 
   /** A (term or type) parameter to a class or method */
   final val Param     = commonFlag(8, "<param>")
@@ -411,7 +412,7 @@ object Flags {
 
   /** Flags guaranteed to be set upon symbol creation */
   final val FromStartFlags =
-    AccessFlags | Module | Package | Deferred | MethodCommon | Param | Scala2ExistentialCommon | Touched |
+    AccessFlags | Module | Package | Deferred | MethodOrHKCommon | Param | Scala2ExistentialCommon | Touched |
     Static | CovariantCommon | ContravariantCommon | ExpandedName | AccessorOrSealed |
     CaseAccessorOrTypeArgument | Frozen | Erroneous | ImplicitCommon | Permanent | SelfNameOrImplClass
 

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

@@ -33,7 +33,7 @@ trait Hashable {
   private def finishHash(hashCode: Int, arity: Int): Int =
     avoidNotCached(hashing.finalizeHash(hashCode, arity))
 
-  protected final def identityHash = avoidNotCached(System.identityHashCode(this))
+  final def identityHash = avoidNotCached(System.identityHashCode(this))
 
   private def finishHash(seed: Int, arity: Int, tp: Type): Int = {
     val elemHash = tp.hash

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

@@ -66,13 +66,13 @@ object NameOps {
     def isSingletonName = name endsWith SINGLETON_SUFFIX
     def isModuleClassName = name endsWith MODULE_SUFFIX
     def isImportName = name startsWith IMPORT
-    def isInheritedName = name.head == '(' && name.startsWith(nme.INHERITED)
+    def isInheritedName = name.length > 0 && name.head == '(' && name.startsWith(nme.INHERITED)
 
     def isModuleVarName(name: Name): Boolean =
       name.stripAnonNumberSuffix endsWith MODULE_VAR_SUFFIX
 
     /** Is name a variable name? */
-    def isVariableName: Boolean = {
+    def isVariableName: Boolean = name.length > 0 && {
       val first = name.head
       (((first.isLower && first.isLetter) || first == '_')
         && (name != false_)
@@ -84,16 +84,17 @@ object NameOps {
       case raw.NE | raw.LE | raw.GE | EMPTY =>
         false
       case _ =>
-        name.last == '=' && name.head != '=' && isOperatorPart(name.head)
+        name.length > 0 && name.last == '=' && name.head != '=' && isOperatorPart(name.head)
     }
 
-    /** Is this the name of a higher-kinded type parameter? */
-    def isHkParamName: Boolean = name(0) == '_' && name.startsWith(HK_PARAM_PREFIX)
+    /** Is this the name of a higher-kinded type parameter of a Lambda? */
+    def isLambdaArgName =
+      name.length > 0 && name.head == tpnme.LAMBDA_ARG_PREFIXhead && name.startsWith(tpnme.LAMBDA_ARG_PREFIX)
 
     /** The index of the higher-kinded type parameter with this name.
-     *  Pre: isHkParamName.
+     *  Pre: isLambdaArgName.
      */
-    def hkParamIndex: Int = name.drop(name.lastIndexOf('$') + 1).toString.toInt
+    def lambdaArgIndex: Int = name.drop(name.lastIndexOf('$') + 1).toString.toInt
 
     /** If the name ends with $nn where nn are
       * all digits, strip the $ and the digits.
@@ -177,19 +178,6 @@ object NameOps {
       }
     }
 
-    /** The variances of the higherKinded parameters of the trait named
-     *  by this name.
-     *  @pre The name is a higher-kinded trait name, i.e. it starts with HK_TRAIT_PREFIX
-     */
-    def hkVariances: List[Int] = {
-      def varianceOfSuffix(suffix: Char): Int = {
-        val idx = tpnme.varianceSuffixes.indexOf(suffix)
-        assert(idx >= 0)
-        idx - 1
-      }
-      name.drop(tpnme.HK_TRAIT_PREFIX.length).toList.map(varianceOfSuffix)
-    }
-
     /** The name of the generic runtime operation corresponding to an array operation */
     def genericArrayOp: TermName = name match {
       case nme.apply => nme.array_apply

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

@@ -166,6 +166,8 @@ object StdNames {
     final val WILDCARD_STAR: N                  = "_*"
     final val REIFY_TREECREATOR_PREFIX: N       = "$treecreator"
     final val REIFY_TYPECREATOR_PREFIX: N       = "$typecreator"
+    final val LAMBDA_ARG_PREFIX: N              = "$hkArg$"
+    final val LAMBDA_ARG_PREFIXhead: Char       = LAMBDA_ARG_PREFIX.head
 
     final val Any: N             = "Any"
     final val AnyVal: N          = "AnyVal"
@@ -249,8 +251,6 @@ object StdNames {
     val SKOLEM: N                   = "<skolem>"
     val SPECIALIZED_INSTANCE: N     = "specInstance$"
     val THIS: N                     = "_$this"
-    val HK_PARAM_PREFIX: N          = "_$hk$"
-    val HK_TRAIT_PREFIX: N          = "$HigherKinded$"
 
     final val Nil: N                = "Nil"
     final val Predef: N             = "Predef"
@@ -286,6 +286,7 @@ object StdNames {
     val Flag : N                = "Flag"
     val Ident: N                = "Ident"
     val Import: N               = "Import"
+    val LambdaPrefix: N         = "Lambda$"
     val Literal: N              = "Literal"
     val LiteralAnnotArg: N      = "LiteralAnnotArg"
     val Modifiers: N            = "Modifiers"
@@ -645,8 +646,8 @@ object StdNames {
     def syntheticTypeParamNames(num: Int): List[TypeName] =
       (0 until num).map(syntheticTypeParamName)(breakOut)
 
-    def higherKindedTraitName(vcs: List[Int]): TypeName = HK_TRAIT_PREFIX ++ vcs.map(varianceSuffix).mkString
-    def higherKindedParamName(n: Int) = HK_PARAM_PREFIX ++ n.toString
+    def lambdaTraitName(vcs: List[Int]): TypeName = LambdaPrefix ++ vcs.map(varianceSuffix).mkString
+    def lambdaArgName(n: Int) = LAMBDA_ARG_PREFIX ++ n.toString
 
     final val Conforms = encode("<:<")
 

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

@@ -321,9 +321,17 @@ object SymDenotations {
     final def isAnonymousClass(implicit ctx: Context): Boolean =
       initial.asSymDenotation.name startsWith tpnme.ANON_CLASS
 
+    /** Is this symbol a class representing a refinement? These classes
+     *  are used only temporarily in Typer and Unpickler as an intermediate
+     *  step for creating Refinement types.
+     */
     final def isRefinementClass(implicit ctx: Context): Boolean =
       name.decode == tpnme.REFINE_CLASS
 
+    /** is this symbol a trait representing a type lambda? */
+    final def isLambdaTrait(implicit ctx: Context): Boolean =
+      isClass && name.startsWith(tpnme.LambdaPrefix)
+
     /** Is this symbol a package object or its module class? */
     def isPackageObject(implicit ctx: Context): Boolean = {
       val poName = if (isType) nme.PACKAGE_CLS else nme.PACKAGE
@@ -699,7 +707,7 @@ object SymDenotations {
 
     /** All symbols overriden by this denotation. */
     final def allOverriddenSymbols(implicit ctx: Context): Iterator[Symbol] =
-      if (exists)
+      if (exists && owner.isClass)
         owner.info.baseClasses.tail.iterator map overriddenSymbol filter (_.exists)
       else
         Iterator.empty