Add new pattern matcher

Author: odersky

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -63,6 +63,7 @@ class Compiler {
            new HoistSuperArgs,      // Hoist complex arguments of supercalls to enclosing scope
            new ClassOf),            // Expand `Predef.classOf` calls.
       List(new TryCatchPatterns,    // Compile cases in try/catch
+           new PatMat,
            new PatternMatcher,      // Compile pattern matches
            new ExplicitOuter,       // Add accessors to outer classes from nested ones.
            new ExplicitSelf,        // Make references to non-trivial self types explicit as casts

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -682,6 +682,12 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
     def select(name: Name)(implicit ctx: Context): Select =
       Select(tree, name)
 
+    /** A select node with the given selector name such that the designated
+     *  member satisfies predicate `p`. Useful for disambiguating overloaded members.
+     */
+    def select(name: Name, p: Symbol => Boolean)(implicit ctx: Context): Select =
+      select(tree.tpe.member(name).suchThat(p).symbol)
+
     /** A select node with the given type */
     def select(tp: NamedType)(implicit ctx: Context): Select =
       untpd.Select(tree, tp.name).withType(tp)

compiler/src/dotty/tools/dotc/config/Printers.scala

@@ -32,5 +32,6 @@ object Printers {
   val pickling: Printer = noPrinter
   val inlining: Printer = noPrinter
   val exhaustivity: Printer = noPrinter
+  val patmatch: Printer = new Printer
   val simplify: Printer = noPrinter
 }

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

@@ -373,6 +373,10 @@ class Definitions {
     def Seq_apply(implicit ctx: Context) = Seq_applyR.symbol
     lazy val Seq_headR = SeqClass.requiredMethodRef(nme.head)
     def Seq_head(implicit ctx: Context) = Seq_headR.symbol
+    lazy val Seq_dropR = SeqClass.requiredMethodRef(nme.drop)
+    def Seq_drop(implicit ctx: Context) = Seq_dropR.symbol
+    lazy val Seq_lengthCompareR = SeqClass.requiredMethodRef(nme.lengthCompare)
+    def Seq_lengthCompare(implicit ctx: Context) = Seq_lengthCompareR.symbol
 
   lazy val ArrayType: TypeRef = ctx.requiredClassRef("scala.Array")
   def ArrayClass(implicit ctx: Context) = ArrayType.symbol.asClass