Package java_cup

Class lalr_item_set

java.lang.Object
java_cup.lalr_item_set

public class lalr_item_set extends Object
This class represents a set of LALR items. For purposes of building these sets, items are considered unique only if they have unique cores (i.e., ignoring differences in their lookahead sets).

This class provides fairly conventional set oriented operations (union, sub/super-set tests, etc.), as well as an LALR "closure" operation (see compute_closure()).

See Also:
  • Field Details

    • _all

      protected Hashtable _all
      A hash table to implement the set. We store the items using themselves as keys.
    • hashcode_cache

      protected Integer hashcode_cache
      Cached hashcode for this set.
  • Constructor Details

    • lalr_item_set

      public lalr_item_set()
      Constructor for an empty set.
    • lalr_item_set

      public lalr_item_set(lalr_item_set other) throws internal_error
      Constructor for cloning from another set.
      Parameters:
      other - indicates set we should copy from.
      Throws:
      internal_error
  • Method Details

    • all

      public Enumeration all()
      Access to all elements of the set.
    • size

      public int size()
      Size of the set
    • contains

      public boolean contains(lalr_item itm)
      Does the set contain a particular item?
      Parameters:
      itm - the item in question.
    • find

      public lalr_item find(lalr_item itm)
      Return the item in the set matching a particular item (or null if not found)
      Parameters:
      itm - the item we are looking for.
    • is_subset_of

      public boolean is_subset_of(lalr_item_set other) throws internal_error
      Is this set an (improper) subset of another?
      Parameters:
      other - the other set in question.
      Throws:
      internal_error
    • is_superset_of

      public boolean is_superset_of(lalr_item_set other) throws internal_error
      Is this set an (improper) superset of another?
      Parameters:
      other - the other set in question.
      Throws:
      internal_error
    • add

      public lalr_item add(lalr_item itm) throws internal_error
      Add a singleton item, merging lookahead sets if the item is already part of the set. returns the element of the set that was added or merged into.
      Parameters:
      itm - the item being added.
      Throws:
      internal_error
    • remove

      public void remove(lalr_item itm) throws internal_error
      Remove a single item if it is in the set.
      Parameters:
      itm - the item to remove.
      Throws:
      internal_error
    • add

      public void add(lalr_item_set other) throws internal_error
      Add a complete set, merging lookaheads where items are already in the set
      Parameters:
      other - the set to be added.
      Throws:
      internal_error
    • remove

      public void remove(lalr_item_set other) throws internal_error
      Remove (set subtract) a complete set.
      Parameters:
      other - the set to remove.
      Throws:
      internal_error
    • get_one

      public lalr_item get_one() throws internal_error
      Remove and return one item from the set (done in hash order).
      Throws:
      internal_error
    • not_null

      protected void not_null(Object obj) throws internal_error
      Helper function for null test. Throws an interal_error exception if its parameter is null.
      Parameters:
      obj - the object we are testing.
      Throws:
      internal_error
    • compute_closure

      public void compute_closure() throws internal_error
      Compute the closure of the set using the LALR closure rules. Basically for every item of the form:
          [L ::= a *N alpha, l] 
        
      (where N is a a non terminal and alpha is a string of symbols) make sure there are also items of the form:
          [N ::= *beta, first(alpha l)] 
        
      corresponding to each production of N. Items with identical cores but differing lookahead sets are merged by creating a new item with the same core and the union of the lookahead sets (the LA in LALR stands for "lookahead merged" and this is where the merger is). This routine assumes that nullability and first sets have been computed for all productions before it is called.
      Throws:
      internal_error
    • equals

      public boolean equals(lalr_item_set other)
      Equality comparison.
    • equals

      public boolean equals(Object other)
      Generic equality comparison.
      Overrides:
      equals in class Object
    • hashCode

      public int hashCode()
      Return hash code.
      Overrides:
      hashCode in class Object
    • toString

      public String toString()
      Convert to string.
      Overrides:
      toString in class Object