Scala example source code file (SemiLattice.scala)

This example Scala source code file (SemiLattice.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

any, anyref, boolean, compiler, elem, istate, list, lub, nsc, s, string, traversableonce

The SemiLattice.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala.tools.nsc
package backend.icode
package analysis

/** A complete lattice.
 */
trait SemiLattice {
  type Elem <: AnyRef

  /** Hold together local variable and stack state. The
   *  equals method uses reference equality for top and bottom,
   *  and structural equality for other values.
   */
  final case class IState[V, S](vars: V, stack: S) {
    override def hashCode = vars.hashCode + stack.hashCode
    override def equals(other: Any): Boolean = other match {
      case x: IState[_, _]  =>
        if ((this eq bottom) || (this eq top) || (x eq bottom) || (x eq top)) this eq x
        else stack == x.stack && vars == x.vars
      case _ =>
        false
    }
    private def tstring(x: Any): String = x match {
      case xs: TraversableOnce[_] => xs map tstring mkString " "
      case _                      => "" + x
    }
    override def toString = "IState(" + tstring(vars) + ", " + tstring(stack) + ")"
  }

  /** Return the least upper bound of a and b. */
  def lub2(exceptional: Boolean)(a: Elem, b: Elem): Elem

  /** Return the top element. */
  def top: Elem

  /** Return the bottom element. */
  def bottom: Elem

  /** Compute the least upper bound of a list of elements. */
  def lub(xs: List[Elem], exceptional: Boolean): Elem =
    if (xs.isEmpty) bottom
    else try xs reduceLeft lub2(exceptional)
    catch { case e: LubException  => Console.println("Lub on blocks: " + xs) ; throw e }
}