|
|||||||||
| Home >> All >> [ java_cup overview ] | PREV CLASS NEXT CLASS | ||||||||
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD |
DETAIL: FIELD | CONSTR | METHOD | ||||||||
java_cup
Class lalr_state
java.lang.Objectjava_cup.lalr_state
- public class lalr_state
- extends java.lang.Object
This class represents a state in the LALR viable prefix recognition machine. A state consists of an LALR item set and a set of transitions to other states under terminal and non-terminal symbols. Each state represents a potential configuration of the parser. If the item set of a state includes an item such as:
[A ::= B * C d E , {a,b,c}]
this indicates that when the parser is in this state it is currently
looking for an A of the given form, has already seen the B, and would
expect to see an a, b, or c after this sequence is complete. Note that
the parser is normally looking for several things at once (represented
by several items). In our example above, the state would also include
items such as:
[C ::= * X e Z, {d}]
[X ::= * f, {e}]
to indicate that it was currently looking for a C followed by a d (which
would be reduced into a C, matching the first symbol in our production
above), and the terminal f followed by e.At runtime, the parser uses a viable prefix recognition machine made up of these states to parse. The parser has two operations, shift and reduce. In a shift, it consumes one Symbol and makes a transition to a new state. This corresponds to "moving the dot past" a terminal in one or more items in the state (these new shifted items will then be found in the state at the end of the transition). For a reduce operation, the parser is signifying that it is recognizing the RHS of some production. To do this it first "backs up" by popping a stack of previously saved states. It pops off the same number of states as are found in the RHS of the production. This leaves the machine in the same state is was in when the parser first attempted to find the RHS. From this state it makes a transition based on the non-terminal on the LHS of the production. This corresponds to placing the parse in a configuration equivalent to having replaced all the symbols from the the input corresponding to the RHS with the symbol on the LHS.
- Version:
- last updated: 7/3/96
| Field Summary | |
protected static java.util.Hashtable |
_all
Collection of all states. |
protected static java.util.Hashtable |
_all_kernels
Hash table to find states by their kernels (i.e, the original, unclosed, set of items -- which uniquely define the state). |
protected int |
_index
Index of this state in the parse tables |
protected lalr_item_set |
_items
The item set for this state. |
protected lalr_transition |
_transitions
List of transitions out of this state. |
protected static int |
next_index
Static counter for assigning unique state indexes. |
| Constructor Summary | |
lalr_state(lalr_item_set itms)
Constructor for building a state from a set of items. |
|
| Method Summary | |
void |
add_transition(symbol on_sym,
lalr_state to_st)
Add a transition out of this state to another. |
static java.util.Enumeration |
all()
Collection of all states. |
static lalr_state |
build_machine(production start_prod)
Build an LALR viable prefix recognition machine given a start production. |
void |
build_table_entries(parse_action_table act_table,
parse_reduce_table reduce_table)
Fill in the parse table entries for this state. |
protected static void |
dump_state(lalr_state st)
Helper routine for debugging -- produces a dump of the given state onto System.out. |
boolean |
equals(lalr_state other)
Equality comparison. |
boolean |
equals(java.lang.Object other)
Generic equality comparison. |
static lalr_state |
find_state(lalr_item_set itms)
Find and return state with a given a kernel item set (or null if not found). |
protected boolean |
fix_with_precedence(production p,
int term_index,
parse_action_row table_row,
parse_action act)
Procedure that attempts to fix a shift/reduce error by using precedences. |
int |
hashCode()
Produce a hash code. |
int |
index()
Index of this state in the parse tables |
protected parse_action |
insert_action(parse_action a1,
parse_action a2,
int act_type)
|
protected parse_action |
insert_reduce(parse_action a1,
parse_action a2)
|
protected parse_action |
insert_shift(parse_action a1,
parse_action a2)
|
lalr_item_set |
items()
The item set for this state. |
static int |
number()
Indicate total number of states there are. |
protected static void |
propagate_all_lookaheads()
Propagate lookahead sets through the constructed viable prefix recognizer. |
protected void |
propagate_lookaheads()
Propagate lookahead sets out of this state. |
protected void |
report_conflicts(terminal_set conflict_set)
Produce warning messages for all conflicts found in this state. |
protected void |
report_reduce_reduce(lalr_item itm1,
lalr_item itm2)
Produce a warning message for one reduce/reduce conflict. |
protected void |
report_shift_reduce(lalr_item red_itm,
int conflict_sym)
Produce a warning message for one shift/reduce conflict. |
java.lang.String |
toString()
Convert to a string. |
lalr_transition |
transitions()
List of transitions out of this state. |
| Methods inherited from class java.lang.Object |
clone, finalize, getClass, notify, notifyAll, wait, wait, wait |
| Field Detail |
_all
protected static java.util.Hashtable _all
- Collection of all states.
_all_kernels
protected static java.util.Hashtable _all_kernels
- Hash table to find states by their kernels (i.e, the original,
unclosed, set of items -- which uniquely define the state). This table
stores state objects using (a copy of) their kernel item sets as keys.
next_index
protected static int next_index
- Static counter for assigning unique state indexes.
_items
protected lalr_item_set _items
- The item set for this state.
_transitions
protected lalr_transition _transitions
- List of transitions out of this state.
_index
protected int _index
- Index of this state in the parse tables
| Constructor Detail |
lalr_state
public lalr_state(lalr_item_set itms) throws internal_error
- Constructor for building a state from a set of items.
| Method Detail |
all
public static java.util.Enumeration all()
- Collection of all states.
number
public static int number()
- Indicate total number of states there are.
find_state
public static lalr_state find_state(lalr_item_set itms)
- Find and return state with a given a kernel item set (or null if not
found). The kernel item set is the subset of items that were used to
originally create the state. These items are formed by "shifting the
dot" within items of other states that have a transition to this one.
The remaining elements of this state's item set are added during closure.
items
public lalr_item_set items()
- The item set for this state.
transitions
public lalr_transition transitions()
- List of transitions out of this state.
index
public int index()
- Index of this state in the parse tables
dump_state
protected static void dump_state(lalr_state st) throws internal_error
- Helper routine for debugging -- produces a dump of the given state
onto System.out.
propagate_all_lookaheads
protected static void propagate_all_lookaheads()
throws internal_error
- Propagate lookahead sets through the constructed viable prefix
recognizer. When the machine is constructed, each item that results
in the creation of another such that its lookahead is included in the
other's will have a propagate link set up for it. This allows additions
to the lookahead of one item to be included in other items that it
was used to directly or indirectly create.
add_transition
public void add_transition(symbol on_sym, lalr_state to_st) throws internal_error
- Add a transition out of this state to another.
build_machine
public static lalr_state build_machine(production start_prod) throws internal_error
- Build an LALR viable prefix recognition machine given a start
production. This method operates by first building a start state
from the start production (based on a single item with the dot at
the beginning and EOF as expected lookahead). Then for each state
it attempts to extend the machine by creating transitions out of
the state to new or existing states. When considering extension
from a state we make a transition on each symbol that appears before
the dot in some item. For example, if we have the items:
[A ::= a b * X c, {d,e}] [B ::= a b * X d, {a,b}]in some state, then we would be making a transition under X to a new state. This new state would be formed by a "kernel" of items corresponding to moving the dot past the X. In this case:[A ::= a b X * c, {d,e}] [B ::= a b X * Y, {a,b}]The full state would then be formed by "closing" this kernel set of items so that it included items that represented productions of things the parser was now looking for. In this case we would items corresponding to productions of Y, since various forms of Y are expected next when in this state (see lalr_item_set.compute_closure() for details on closure).The process of building the viable prefix recognizer terminates when no new states can be added. However, in order to build a smaller number of states (i.e., corresponding to LALR rather than canonical LR) the state building process does not maintain full loookaheads in all items. Consequently, after the machine is built, we go back and propagate lookaheads through the constructed machine using a call to propagate_all_lookaheads(). This makes use of propagation links constructed during the closure and transition process.
propagate_lookaheads
protected void propagate_lookaheads()
throws internal_error
- Propagate lookahead sets out of this state. This recursively
propagates to all items that have propagation links from some item
in this state.
build_table_entries
public void build_table_entries(parse_action_table act_table, parse_reduce_table reduce_table) throws internal_error
- Fill in the parse table entries for this state. There are two
parse tables that encode the viable prefix recognition machine, an
action table and a reduce-goto table. The rows in each table
correspond to states of the machine. The columns of the action table
are indexed by terminal symbols and correspond to either transitions
out of the state (shift entries) or reductions from the state to some
previous state saved on the stack (reduce entries). All entries in the
action table that are not shifts or reduces, represent errors. The
reduce-goto table is indexed by non terminals and represents transitions
out of a state on that non-terminal.
Conflicts occur if more than one action needs to go in one entry of the action table (this cannot happen with the reduce-goto table). Conflicts are resolved by always shifting for shift/reduce conflicts and choosing the lowest numbered production (hence the one that appeared first in the specification) in reduce/reduce conflicts. All conflicts are reported and if more conflicts are detected than were declared by the user, code generation is aborted.
fix_with_precedence
protected boolean fix_with_precedence(production p, int term_index, parse_action_row table_row, parse_action act) throws internal_error
- Procedure that attempts to fix a shift/reduce error by using
precedences. --frankf 6/26/96
if a production (also called rule) or the lookahead terminal
has a precedence, then the table can be fixed. if the rule
has greater precedence than the terminal, a reduce by that rule
in inserted in the table. If the terminal has a higher precedence,
it is shifted. if they have equal precedence, then the associativity
of the precedence is used to determine what to put in the table:
if the precedence is left associative, the action is to reduce.
if the precedence is right associative, the action is to shift.
if the precedence is non associative, then it is a syntax error.
insert_action
protected parse_action insert_action(parse_action a1, parse_action a2, int act_type) throws internal_error
insert_shift
protected parse_action insert_shift(parse_action a1, parse_action a2) throws internal_error
insert_reduce
protected parse_action insert_reduce(parse_action a1, parse_action a2) throws internal_error
report_conflicts
protected void report_conflicts(terminal_set conflict_set) throws internal_error
- Produce warning messages for all conflicts found in this state.
report_reduce_reduce
protected void report_reduce_reduce(lalr_item itm1, lalr_item itm2) throws internal_error
- Produce a warning message for one reduce/reduce conflict.
report_shift_reduce
protected void report_shift_reduce(lalr_item red_itm, int conflict_sym) throws internal_error
- Produce a warning message for one shift/reduce conflict.
equals
public boolean equals(lalr_state other)
- Equality comparison.
equals
public boolean equals(java.lang.Object other)
- Generic equality comparison.
hashCode
public int hashCode()
- Produce a hash code.
toString
public java.lang.String toString()
- Convert to a string.
|
|||||||||
| Home >> All >> [ java_cup overview ] | PREV CLASS NEXT CLASS | ||||||||
|
SUMMARY: JAVADOC | SOURCE | DOWNLOAD | NESTED | FIELD | CONSTR | METHOD |
DETAIL: FIELD | CONSTR | METHOD | ||||||||