Package com.aquima.interactions.java_cup

Class virtual_parse_stack

java.lang.Object
com.aquima.interactions.java_cup.virtual_parse_stack
public class virtual_parse_stack extends Object
This class implements a temporary or "virtual" parse stack that replaces the top portion of the actual parse stack (the part that has been changed by some set of operations) while maintaining its original contents. This data structure is used when the parse needs to "parse ahead" to determine if a given error recovery attempt will allow the parse to continue far enough to consider it successful. Once success or failure of parse ahead is determined the system then reverts to the original parse stack (which has not actually been modified). Since parse ahead does not execute actions, only parse state is maintained on the virtual stack, not full Symbol objects.
Version:
last updated: 7/3/96
Author:
Frank Flannery
See Also:
  • invalid reference 
    java_cup.runtime.lr_parser

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    protected int
    real_next
    Top of stack indicator for where we leave off in the real stack.
    protected Stack<Symbol>
    real_stack
    The real stack that we shadow.
    protected Stack<Integer>
    vstack
    The virtual top portion of the stack.

  • Constructor Summary

    Constructors
    Constructor
    Description
    virtual_parse_stack(Stack<Symbol> shadowing_stack)
    Constructor to build a virtual stack out of a real stack.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    empty()
    Indicate whether the stack is empty.
    protected void
    get_from_real()
    Transfer an element from the real to the virtual stack.
    void
    pop()
    Pop the stack.
    void
    push(int state_num)
    Push a state number onto the stack.
    int
    top()
    Return value on the top of the stack (without popping it).

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • real_stack

      protected Stack<Symbol> real_stack
      The real stack that we shadow. This is accessed when we move off the bottom of the virtual portion of the stack, but is always left unmodified.

    • real_next

      protected int real_next
      Top of stack indicator for where we leave off in the real stack. This is measured from top of stack, so 0 would indicate that no elements have been "moved" from the real to virtual stack.

    • vstack

      protected Stack<Integer> vstack
      The virtual top portion of the stack. This stack contains Integer objects with state numbers. This stack shadows the top portion of the real stack within the area that has been modified (via operations on the virtual stack). When this portion of the stack becomes empty we transfer elements from the underlying stack onto this stack.

  • Constructor Details

    • virtual_parse_stack

      public virtual_parse_stack(Stack<Symbol> shadowing_stack) throws Exception
      Constructor to build a virtual stack out of a real stack.
      Throws:
      Exception

  • Method Details

    • get_from_real

      protected void get_from_real()
      Transfer an element from the real to the virtual stack. This assumes that the virtual stack is currently empty.

    • empty

      public boolean empty()
      Indicate whether the stack is empty.

    • top

      public int top() throws Exception
      Return value on the top of the stack (without popping it).
      Throws:
      Exception

    • pop

      public void pop() throws Exception
      Pop the stack.
      Throws:
      Exception

    • push

      public void push(int state_num)
      Push a state number onto the stack.