Streamlining skolemization, specialization.

Skolemization code doesn't belong in Typers.  I carved
out a little place for it.  Also simplifications in
specialization.

Author: paulp

src/compiler/scala/reflect/internal/ExistentialsAndSkolems.scala

@@ -0,0 +1,50 @@
+/* NSC -- new scala compiler
+ * Copyright 2005-2011 LAMP/EPFL
+ * @author  Martin Odersky
+ */
+
+package scala.reflect
+package internal
+
+import scala.collection.{ mutable, immutable }
+import util._
+
+/** The name of this trait defines the eventual intent better than
+ *  it does the initial contents.
+ */
+trait ExistentialsAndSkolems {
+  self: SymbolTable =>
+  
+  /** Map a list of type parameter symbols to skolemized symbols, which
+   *  can be deskolemized to the original type parameter. (A skolem is a
+   *  representation of a bound variable when viewed inside its scope.)
+   *  !!!Adriaan: this does not work for hk types.
+   */
+  def deriveFreshSkolems(tparams: List[Symbol]): List[Symbol] = {
+    class Deskolemizer extends LazyType {
+      override val typeParams = tparams
+      val typeSkolems  = typeParams map (_.newTypeSkolem setInfo this)
+      override def complete(sym: Symbol) {
+        // The info of a skolem is the skolemized info of the
+        // actual type parameter of the skolem
+        sym setInfo sym.deSkolemize.info.substSym(typeParams, typeSkolems)
+      }
+    }
+    (new Deskolemizer).typeSkolems
+  }
+
+  /** Convert to corresponding type parameters all skolems of method
+   *  parameters which appear in `tparams`.
+   */
+  def deskolemizeTypeParams(tparams: List[Symbol])(tp: Type): Type = {
+    class DeSkolemizeMap extends TypeMap {
+      def apply(tp: Type): Type = tp match {
+        case TypeRef(pre, sym, args) if sym.isTypeSkolem && (tparams contains sym.deSkolemize) =>
+          mapOver(typeRef(NoPrefix, sym.deSkolemize, args))
+        case _ =>
+          mapOver(tp)
+      }
+    }
+    new DeSkolemizeMap mapOver tp
+  }
+}

src/compiler/scala/reflect/internal/SymbolTable.scala

@@ -15,6 +15,7 @@ abstract class SymbolTable extends api.Universe
                               with Symbols
                               with Types
                               with Kinds
+                              with ExistentialsAndSkolems
                               with Scopes
                               with Definitions
                               with Constants

src/compiler/scala/reflect/internal/Symbols.scala

@@ -2714,6 +2714,8 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
    */
   def cloneSymbolsAndModify(syms: List[Symbol], infoFn: Type => Type): List[Symbol] =
     cloneSymbols(syms) map (_ modifyInfo infoFn)
+  def cloneSymbolsAtOwnerAndModify(syms: List[Symbol], owner: Symbol, infoFn: Type => Type): List[Symbol] =
+    cloneSymbolsAtOwner(syms, owner) map (_ modifyInfo infoFn)
 
   /** Functions which perform the standard clone/substituting on the given symbols and type,
    *  then call the creator function with the new symbols and type as arguments.

src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala

@@ -1226,18 +1226,18 @@ abstract class SpecializeTypes extends InfoTransform with TypingTransformers {
     val body: mutable.Map[Symbol, Tree] = new mutable.HashMap
 
     /** Map a specializable method to its value parameter symbols. */
-    val parameters: mutable.Map[Symbol, List[List[Symbol]]] = new mutable.HashMap
+    val parameters = mutable.HashMap[Symbol, List[Symbol]]()
 
     /** Collect method bodies that are concrete specialized methods.
      */
     class CollectMethodBodies extends Traverser {
       override def traverse(tree: Tree) = tree match {
-        case  DefDef(mods, name, tparams, vparamss, tpt, rhs) =>
+        case DefDef(mods, name, tparams, vparams :: Nil, tpt, rhs) =>
           if (concreteSpecMethods(tree.symbol) || tree.symbol.isConstructor) {
             debuglog("!!! adding body of a defdef %s, symbol %s: %s".format(tree, tree.symbol, rhs))
             body(tree.symbol) = rhs
             //          body(tree.symbol) = tree // whole method
-            parameters(tree.symbol) = mmap(vparamss)(_.symbol)
+            parameters(tree.symbol) = vparams.map(_.symbol)
             concreteSpecMethods -= tree.symbol
           } // no need to descend further down inside method bodies
 
@@ -1531,12 +1531,6 @@ abstract class SpecializeTypes extends InfoTransform with TypingTransformers {
       }
     }
 
-    private def reskolemize(tparams: List[TypeDef]): (List[Symbol], List[Symbol]) = {
-      val saved = tparams map (_.symbol)
-      localTyper skolemizeTypeParams tparams
-      (saved, tparams map (_.symbol))
-    }
-
     private def duplicateBody(tree: DefDef, source: Symbol) = {
       val symbol = tree.symbol
       val meth   = addBody(tree, source)
@@ -1560,36 +1554,37 @@ abstract class SpecializeTypes extends InfoTransform with TypingTransformers {
      */
     private def addBody(tree: DefDef, source: Symbol): DefDef = {
       val symbol = tree.symbol
-      debuglog("specializing body of" + symbol.fullName + ": " + symbol.info)
-      val DefDef(mods, name, tparams, vparamss, tpt, _) = tree
+      debuglog("specializing body of" + symbol.defString)
+      val DefDef(mods, name, tparams, vparams :: Nil, tpt, _) = tree
 //      val (_, origtparams) = splitParams(source.typeParams)
       val env = typeEnv(symbol)
       val boundTvars = env.keySet
       val origtparams = source.typeParams.filter(tparam => !boundTvars(tparam) || !isScalaValueType(env(tparam)))
       debuglog("substituting " + origtparams + " for " + symbol.typeParams)
 
       // skolemize type parameters
-      val (oldtparams, newtparams) = reskolemize(tparams)
+      val oldtparams = tparams map (_.symbol)
+      val newtparams = deriveFreshSkolems(oldtparams)
+      map2(tparams, newtparams)(_ setSymbol _)
 
       // create fresh symbols for value parameters to hold the skolem types
-      val vparamss1 = List(for (vdef <- vparamss.head; param = vdef.symbol) yield {
-        ValDef(param cloneSymbol symbol substInfo (oldtparams, newtparams))
-      })
+      val newSyms = cloneSymbolsAtOwnerAndModify(vparams map (_.symbol), symbol, _.substSym(oldtparams, newtparams))
 
       // replace value and type parameters of the old method with the new ones
       // log("Adding body for " + tree.symbol + " - origtparams: " + origtparams + "; tparams: " + tparams)
       // log("Type vars of: " + source + ": " + source.typeParams)
       // log("Type env of: " + tree.symbol + ": " + boundTvars)
       // log("newtparams: " + newtparams)
       val symSubstituter = new ImplementationAdapter(
-        parameters(source).flatten ::: origtparams,
-        vparamss1.flatten.map(_.symbol) ::: newtparams,
+        parameters(source) ::: origtparams,
+        newSyms ::: newtparams,
         source.enclClass,
         false) // don't make private fields public
-      val tmp = symSubstituter(body(source).duplicate)
+
+      val newBody = symSubstituter(body(source).duplicate)
       tpt.tpe = tpt.tpe.substSym(oldtparams, newtparams)
 
-      treeCopy.DefDef(tree, mods, name, tparams, vparamss1, tpt, tmp)
+      treeCopy.DefDef(tree, mods, name, tparams, List(newSyms map ValDef), tpt, newBody)
     }
 
     /** Create trees for specialized members of 'sClass', based on the
@@ -1610,9 +1605,9 @@ abstract class SpecializeTypes extends InfoTransform with TypingTransformers {
         if (m.isMethod)  {
           if (info(m).target.hasAccessorFlag) hasSpecializedFields = true
           if (m.isClassConstructor) {
-            val origParamss = parameters(info(m).target)
+            val origParams = parameters(info(m).target)
             val vparams = (
-              map2(m.info.paramTypes, origParamss(0))((tp, sym) =>
+              map2(m.info.paramTypes, origParams)((tp, sym) =>
                 m.newValue(specializedName(sym, typeEnv(sClass)), sym.pos, sym.flags) setInfo tp
               )
             )

src/compiler/scala/tools/nsc/typechecker/Namers.scala

@@ -1299,7 +1299,7 @@ trait Namers extends MethodSynthesis {
         catch typeErrorHandler(tree, ErrorType)
 
       result match {
-        case PolyType(tparams @ (tp :: _), _) if tp.owner.isTerm => typer.deskolemizeTypeParams(tparams)(result)
+        case PolyType(tparams @ (tp :: _), _) if tp.owner.isTerm => deskolemizeTypeParams(tparams)(result)
         case _                                                   => result
       }
     }
@@ -1439,8 +1439,11 @@ trait Namers extends MethodSynthesis {
     private val ownerSym    = owner.symbol
     override val typeParams = tparams map (_.symbol) //@M
     override val tree       = restp.tree
-    if (ownerSym.isTerm)
-      typer skolemizeTypeParams tparams
+
+    if (ownerSym.isTerm) {
+      val skolems = deriveFreshSkolems(tparams map (_.symbol))
+      map2(tparams, skolems)(_ setSymbol _)
+    }
 
     def completeImpl(sym: Symbol) = {
       // @M an abstract type's type parameters are entered.

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -3036,40 +3036,6 @@ trait Typers extends Modes with Adaptations with PatMatVirtualiser {
       packSymbols(localSyms.toList, normalizedTpe)
     }
 
-    /** Replace type parameters with their TypeSkolems, which can later
-     *  be deskolemized to the original type param. (A skolem is a
-     *  representation of a bound variable when viewed inside its scope)
-     *  !!!Adriaan: this does not work for hk types.
-     */
-    def skolemizeTypeParams(tparams: List[TypeDef]): List[TypeDef] = {
-      class Deskolemizer extends LazyType {
-        override val typeParams = tparams map (_.symbol)
-        val typeSkolems  = typeParams map (_.newTypeSkolem setInfo this)
-        // Replace the symbols
-        def substitute() = map2(tparams, typeSkolems)(_ setSymbol _)
-        override def complete(sym: Symbol) {
-          // The info of a skolem is the skolemized info of the
-          // actual type parameter of the skolem
-          sym setInfo sym.deSkolemize.info.substSym(typeParams, typeSkolems)
-        }
-      }
-      (new Deskolemizer).substitute()
-    }
-    /** Convert to corresponding type parameters all skolems of method
-     *  parameters which appear in `tparams`.
-     */
-    def deskolemizeTypeParams(tparams: List[Symbol])(tp: Type): Type = {
-      class DeSkolemizeMap extends TypeMap {
-        def apply(tp: Type): Type = tp match {
-          case TypeRef(pre, sym, args) if sym.isTypeSkolem && (tparams contains sym.deSkolemize) =>
-            mapOver(typeRef(NoPrefix, sym.deSkolemize, args))
-          case _ =>
-            mapOver(tp)
-        }
-      }
-      new DeSkolemizeMap mapOver tp
-    }
-
     def typedClassOf(tree: Tree, tpt: Tree, noGen: Boolean = false) =
       if (!checkClassType(tpt, true, false) && noGen) tpt
       else atPos(tree.pos)(gen.mkClassOf(tpt.tpe))