root/trunk/ProjectFortress/src/com/sun/fortress/scala_src/typechecker/StaticEnv.scala @ 3905

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    4150 Network Circle, Santa Clara, California 95054, U.S.A.
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package com.sun.fortress.scala_src.typechecker

import com.sun.fortress.nodes.Name
import com.sun.fortress.nodes.Type
import com.sun.fortress.nodes_util.Modifiers

/**
 * Represents an environment that exists during static checking, mapping
 * variable names to some value. Each static environment contains 
 */
trait StaticEnv[T] extends Collection[StaticBinding[T]] {
  
  /** Define Env as the type of the implementing class. */
  type Env <: StaticEnv[T]
  
  /** Define EnvBinding as the type of the bindings. */
  type EnvBinding <: StaticBinding[T]
  
  /**
   * Extend this environment with the bindings immediately contained in the
   * given node.
   * 
   * @param node A node or collection of nodes in which to find bindings.
   * @return A new environment with the bindings of this one and those found in
   *         `node` combined.
   */
  def extendWith(node: Any): Env
  
  /**
   * Gets the value stored for the given variable name, if that binding exists.
   *
   * @param name The name to lookup.
   * @return Some(T) if name:T is a binding. None otherwise.
   */
  def lookup(x: Name): Option[EnvBinding]
  
  /** Same as lookup when treating implementing object as a function. */
  def apply(x: Name): Option[EnvBinding] = lookup(x)
  
  /**
   * Gets the type stored for the given variable name, if that binding exists.
   * 
   * @param name The name to lookup.
   * @return Some(T) if name:T is a binding. None otherwise.
   */
  def getType(x: Name): Option[Type]
  
  /** Make the type on `Collection.elements` more specific. */
  def elements: Iterator[EnvBinding]
}

/**
 * A single empty static environment. There are no bindings at all in this
 * environemnt.
 */
trait EmptyStaticEnv[T] extends StaticEnv[T] {
      
  /** Every call to `lookup` fails. */
  override def lookup(x: Name): Option[EnvBinding] = None
      
  /** Every call to `getType` fails. */
  override def getType(x: Name): Option[Type] = None
  
  // Collection implementation
  override def elements: Iterator[EnvBinding] = Iterator.empty
  override def size: Int = 0
}

/**
 * A nested static environment that contains all the bindings of some parent
 * environment and additionally all the explicitly supplied bindings.
 */
trait NestedStaticEnv[T] extends StaticEnv[T] {
    
  /** A static environment that this one extends. */
  protected val parent: Env {
    // Require that the parent has the same binding type.
    type EnvBinding = NestedStaticEnv.this.EnvBinding
  }
    
  /** The bindings explicitly declared in this environment. */
  protected val bindings: Map[Name, EnvBinding]
  
  /** Find it among `bindings` or else in `parent`. */
  def lookup(x: Name): Option[EnvBinding] = bindings.get(x) match {
    case Some(v) => Some(v)
    case None => parent.lookup(x)
  }
  
  // Collection implementation
  def elements: Iterator[EnvBinding] = parent.elements ++ bindings.values
  def size: Int = parent.size + bindings.size
}

/**
 * Provides functionality for finding bindings in nodes and creating new
 * instances of the environment.
 */
trait StaticEnvCompanion[T] {
  
  /** Define Env as the type of the implementing object's companion class. */
  type Env <: StaticEnv[T]
  
  /** Define EnvBinding as the type of the bindings. */
  type EnvBinding <: StaticBinding[T]
  
  /**
   * Extracts all the _immediate_ bindings for this kind of environment from the
   * given node. If `node` is a collection of nodes, then this method returns
   * the concatenation of all bindings found therein. Any bindings located
   * further inside the node will not be extracted.
   * 
   * @param node A node or collection of nodes in which to extract bindings.
   * @return A collection of all the bindings extracted in the given node.
   */
  protected def extractEnvBindings(node: Any): Collection[EnvBinding]
  
  /**
   * Creates a new instance of the environment containing all the bindings
   * found in the given node.
   * 
   * @param node A node or collection of nodes in which to find bindings.
   * @return A new instance of Env containing these bindings.
   */
  def make(node: Any): Env
}


/**
 * A static environment binding of a variable name to some kind of value.
 * 
 * @param name The variable name for the binding.
 * @param value The bound value for this binding.
 */
abstract class StaticBinding[T](val name: Name, val value: T)

object StaticBinding {
  def unapply[T](b: StaticBinding[T]): Option[(Name, T)] = Some(b.name, b.value)
}