java_cup
Class lalr_item_set
public class lalr_item_set
extends java.lang.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()).
protected Hashtable | _all - A hash table to implement the set.
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protected Integer | hashcode_cache - Cached hashcode for this set.
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lalr_item | add(lalr_item itm) - Add a singleton item, merging lookahead sets if the item is already
part of the set.
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void | add(lalr_item_set other) - Add a complete set, merging lookaheads where items are already in
the set
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Enumeration | all() - Access to all elements of the set.
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void | compute_closure() - Compute the closure of the set using the LALR closure rules.
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boolean | contains(lalr_item itm) - Does the set contain a particular item?
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boolean | equals(Object other) - Generic equality comparison.
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boolean | equals(lalr_item_set other) - Equality comparison.
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lalr_item | find(lalr_item itm) - Return the item in the set matching a particular item (or null if not
found)
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lalr_item | get_one() - Remove and return one item from the set (done in hash order).
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int | hashCode() - Return hash code.
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boolean | is_subset_of(lalr_item_set other) - Is this set an (improper) subset of another?
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boolean | is_superset_of(lalr_item_set other) - Is this set an (improper) superset of another?
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protected void | not_null(Object obj) - Helper function for null test.
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void | remove(lalr_item itm) - Remove a single item if it is in the set.
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void | remove(lalr_item_set other) - Remove (set subtract) a complete set.
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int | size() - Size of the set
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String | toString() - Convert to string.
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_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.
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.
other
- indicates set we should copy from.
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.
itm
- the item being added.
add
public void add(lalr_item_set other)
throws internal_error
Add a complete set, merging lookaheads where items are already in
the set
other
- the set to be added.
all
public Enumeration all()
Access to all elements of the set.
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.
contains
public boolean contains(lalr_item itm)
Does the set contain a particular item?
itm
- the item in question.
equals
public boolean equals(Object other)
Generic equality comparison.
equals
public boolean equals(lalr_item_set other)
Equality comparison.
find
public lalr_item find(lalr_item itm)
Return the item in the set matching a particular item (or null if not
found)
itm
- the item we are looking for.
get_one
public lalr_item get_one()
throws internal_error
Remove and return one item from the set (done in hash order).
hashCode
public int hashCode()
Return hash code.
is_subset_of
public boolean is_subset_of(lalr_item_set other)
throws internal_error
Is this set an (improper) subset of another?
other
- the other set in question.
is_superset_of
public boolean is_superset_of(lalr_item_set other)
throws internal_error
Is this set an (improper) superset of another?
other
- the other set in question.
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.
obj
- the object we are testing.
remove
public void remove(lalr_item itm)
throws internal_error
Remove a single item if it is in the set.
itm
- the item to remove.
remove
public void remove(lalr_item_set other)
throws internal_error
Remove (set subtract) a complete set.
other
- the set to remove.
size
public int size()
Size of the set
toString
public String toString()
Convert to string.