/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Remove (Set subtract) a complete Set.
* @param other the Set we are removing.
*/
public void remove(symbol_set other)
{
not_null(other);
/* walk down the other Set and do the removes individually */
IEnumerator e = other.all();
while (e.MoveNext())
{
remove((symbol)e.Current);
}
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Determine if this Set is an (improper) subset of another.
* @param other the Set we are testing against.
*/
public bool is_subset_of(symbol_set other)
{
not_null(other);
/* walk down our Set and make sure every element is in the other */
IEnumerator e = all();
while ( e.MoveNext() )
if (!other.contains((symbol)e.Current))
return false;
/* they were all there */
return true;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Add (union) in a complete Set.
* @param other the Set we are adding in.
* @return true if this changes the Set.
*/
public bool add(symbol_set other)
{
bool result = false;
not_null(other);
/* walk down the other Set and do the adds individually */
IEnumerator e = other.all();
while (e.MoveNext())
{
result = add((symbol)e.Current) || result;
}
return(result);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Determine if this Set is an (improper) subset of another.
* @param other the Set we are testing against.
*/
public bool is_subset_of(symbol_set other)
{
not_null(other);
/* walk down our Set and make sure every element is in the other */
IEnumerator e = all();
while (e.MoveNext())
{
if (!other.contains((symbol)e.Current))
{
return(false);
}
}
/* they were all there */
return(true);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Equality comparison. */
public bool Equals(symbol_set other)
{
if (other == null || other.size() != size())
{
return(false);
}
/* once we know they are the same size, then improper subset does test */
try
{
return(is_subset_of(other));
}
catch (internal_error e)
{
/* can't throw the error (because super class doesn't), so we crash */
e.crash();
return(false);
}
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Determine if this Set is an (improper) superset of another.
* @param other the Set we are are testing against.
*/
public bool is_superset_of(symbol_set other)
{
not_null(other);
return other.is_subset_of(this);
}
/** Constructor for cloning from another Set.
* @param other the Set we are cloning from.
*/
public symbol_set(symbol_set other)
{
not_null(other);
_all = (Hashtable)other._all.Clone();
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Equality comparison. */
public bool Equals(symbol_set other)
{
if (other == null || other.size() != size()) return false;
/* once we know they are the same size, then improper subset does test */
try
{
return is_subset_of(other);
}
catch (internal_error e)
{
/* can't throw the error (because super class doesn't), so we crash */
e.crash();
return false;
}
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Remove (Set subtract) a complete Set.
* @param other the Set we are removing.
*/
public void remove(symbol_set other)
{
not_null(other);
/* walk down the other Set and do the removes individually */
IEnumerator e = other.all();
while ( e.MoveNext() )
remove((symbol)e.Current);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Add (union) in a complete Set.
* @param other the Set we are adding in.
* @return true if this changes the Set.
*/
public bool add(symbol_set other)
{
bool result = false;
not_null(other);
/* walk down the other Set and do the adds individually */
IEnumerator e = other.all();
while ( e.MoveNext())
result = add((symbol)e.Current) || result;
return result;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** 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: <pre>
* [A ::= a b * X c, {d,e}]
* [B ::= a b * X d, {a,b}]
* </pre>
* 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: <pre>
* [A ::= a b X * c, {d,e}]
* [B ::= a b X * Y, {a,b}]
* </pre>
* 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). <p>
*
* 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.
*
* @param start_prod the start production of the grammar
* @see java_cup.lalr_item_set#compute_closure
* @see java_cup.lalr_state#propagate_all_lookaheads
*/
public static lalr_state build_machine(production start_prod)
{
lalr_state start_state;
lalr_item_set start_items;
lalr_item_set new_items;
lalr_item_set linked_items;
lalr_item_set kernel;
Stack work_stack = new Stack();
lalr_state st, new_st;
symbol_set outgoing;
lalr_item itm, new_itm, existing, fix_itm;
symbol sym, sym2;
IEnumerator i, s, fix;
/* sanity check */
if (start_prod == null)
{
throw new internal_error(
"Attempt to build viable prefix recognizer using a null production");
}
/* build item with dot at front of start production and EOF lookahead */
start_items = new lalr_item_set();
itm = new lalr_item(start_prod);
itm.lookahead().add(terminal.EOF);
start_items.add(itm);
/* create copy the item Set to form the kernel */
kernel = new lalr_item_set(start_items);
/* create the closure from that item Set */
start_items.compute_closure();
/* build a state out of that item Set and put it in our work Set */
start_state = new lalr_state(start_items);
work_stack.Push(start_state);
/* enter the state using the kernel as the key */
_all_kernels.Add(kernel, start_state);
/* continue looking at new states until we have no more work to do */
while (work_stack.Count != 0)
{
/* remove a state from the work Set */
st = (lalr_state)work_stack.Pop();
/* gather up all the symbols that appear before dots */
outgoing = new symbol_set();
i = st.items().all();
while (i.MoveNext())
{
itm = (lalr_item)i.Current;
/* add the symbol before the dot (if any) to our collection */
sym = itm.symbol_after_dot();
if (sym != null)
{
outgoing.add(sym);
}
}
/* now create a transition out for each individual symbol */
s = outgoing.all();
while (s.MoveNext())
{
sym = (symbol)s.Current;
/* will be keeping the Set of items with propagate links */
linked_items = new lalr_item_set();
/* gather up shifted versions of all the items that have this
* symbol before the dot */
new_items = new lalr_item_set();
i = st.items().all();
while (i.MoveNext())
{
itm = (lalr_item)i.Current;
/* if this is the symbol we are working on now, add to Set */
sym2 = itm.symbol_after_dot();
if (sym.Equals(sym2))
{
/* add to the kernel of the new state */
new_items.add(itm.shift());
/* remember that itm has propagate link to it */
linked_items.add(itm);
}
}
/* use new items as state kernel */
kernel = new lalr_item_set(new_items);
/* have we seen this one already? */
new_st = (lalr_state)_all_kernels[kernel];
/* if we haven't, build a new state out of the item Set */
if (new_st == null)
{
/* compute closure of the kernel for the full item Set */
new_items.compute_closure();
/* build the new state */
new_st = new lalr_state(new_items);
/* add the new state to our work Set */
work_stack.Push(new_st);
/* put it in our kernel table */
_all_kernels.Add(kernel, new_st);
}
/* otherwise relink propagation to items in existing state */
else
{
/* walk through the items that have links to the new state */
fix = linked_items.all();
while (fix.MoveNext())
{
fix_itm = (lalr_item)fix.Current;
/* look at each propagate link out of that item */
for (int l = 0; l < fix_itm.propagate_items().Count; l++)
{
/* pull out item linked to in the new state */
new_itm = (lalr_item)fix_itm.propagate_items().ToArray()[l];
/* find corresponding item in the existing state */
existing = new_st.items().find(new_itm);
/* fix up the item so it points to the existing Set */
if (existing != null)
{
fix_itm.set_propagate_item(existing, l);
}
}
}
}
/* add a transition from current state to that state */
st.add_transition(sym, new_st);
}
}
/* all done building states */
/* propagate complete lookahead sets throughout the states */
propagate_all_lookaheads();
return(start_state);
}
/** Constructor for cloning from another Set.
* @param other the Set we are cloning from.
*/
public symbol_set(symbol_set other)
{
not_null(other);
_all = (Hashtable)other._all.Clone();
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Determine if this Set is an (improper) superset of another.
* @param other the Set we are are testing against.
*/
public bool is_superset_of(symbol_set other)
{
not_null(other);
return(other.is_subset_of(this));
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** 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: <pre>
* [A ::= a b * X c, {d,e}]
* [B ::= a b * X d, {a,b}]
* </pre>
* 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: <pre>
* [A ::= a b X * c, {d,e}]
* [B ::= a b X * Y, {a,b}]
* </pre>
* 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). <p>
*
* 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.
*
* @param start_prod the start production of the grammar
* @see java_cup.lalr_item_set#compute_closure
* @see java_cup.lalr_state#propagate_all_lookaheads
*/
public static lalr_state build_machine(production start_prod)
{
lalr_state start_state;
lalr_item_set start_items;
lalr_item_set new_items;
lalr_item_set linked_items;
lalr_item_set kernel;
Stack work_stack = new Stack();
lalr_state st, new_st;
symbol_set outgoing;
lalr_item itm, new_itm, existing, fix_itm;
symbol sym, sym2;
IEnumerator i, s, fix;
/* sanity check */
if (start_prod == null)
throw new internal_error(
"Attempt to build viable prefix recognizer using a null production");
/* build item with dot at front of start production and EOF lookahead */
start_items = new lalr_item_set();
itm = new lalr_item(start_prod);
itm.lookahead().add(terminal.EOF);
start_items.add(itm);
/* create copy the item Set to form the kernel */
kernel = new lalr_item_set(start_items);
/* create the closure from that item Set */
start_items.compute_closure();
/* build a state out of that item Set and put it in our work Set */
start_state = new lalr_state(start_items);
work_stack.Push(start_state);
/* enter the state using the kernel as the key */
_all_kernels.Add(kernel, start_state);
/* continue looking at new states until we have no more work to do */
while (work_stack.Count!=0)
{
/* remove a state from the work Set */
st = (lalr_state)work_stack.Pop();
/* gather up all the symbols that appear before dots */
outgoing = new symbol_set();
i = st.items().all();
while ( i.MoveNext() )
{
itm = (lalr_item)i.Current;
/* add the symbol before the dot (if any) to our collection */
sym = itm.symbol_after_dot();
if (sym != null) outgoing.add(sym);
}
/* now create a transition out for each individual symbol */
s = outgoing.all();
while ( s.MoveNext())
{
sym = (symbol)s.Current;
/* will be keeping the Set of items with propagate links */
linked_items = new lalr_item_set();
/* gather up shifted versions of all the items that have this
symbol before the dot */
new_items = new lalr_item_set();
i = st.items().all();
while ( i.MoveNext())
{
itm = (lalr_item)i.Current;
/* if this is the symbol we are working on now, add to Set */
sym2 = itm.symbol_after_dot();
if (sym.Equals(sym2))
{
/* add to the kernel of the new state */
new_items.add(itm.shift());
/* remember that itm has propagate link to it */
linked_items.add(itm);
}
}
/* use new items as state kernel */
kernel = new lalr_item_set(new_items);
/* have we seen this one already? */
new_st = (lalr_state)_all_kernels[kernel];
/* if we haven't, build a new state out of the item Set */
if (new_st == null)
{
/* compute closure of the kernel for the full item Set */
new_items.compute_closure();
/* build the new state */
new_st = new lalr_state(new_items);
/* add the new state to our work Set */
work_stack.Push(new_st);
/* put it in our kernel table */
_all_kernels.Add(kernel, new_st);
}
/* otherwise relink propagation to items in existing state */
else
{
/* walk through the items that have links to the new state */
fix = linked_items.all();
while ( fix.MoveNext() )
{
fix_itm = (lalr_item)fix.Current;
/* look at each propagate link out of that item */
for (int l =0; l < fix_itm.propagate_items().Count; l++)
{
/* pull out item linked to in the new state */
new_itm =(lalr_item) fix_itm.propagate_items().ToArray()[l];
/* find corresponding item in the existing state */
existing = new_st.items().find(new_itm);
/* fix up the item so it points to the existing Set */
if (existing != null)
{
fix_itm.set_propagate_item(existing,l);
}
}
}
}
/* add a transition from current state to that state */
st.add_transition(sym, new_st);
}
}
/* all done building states */
/* propagate complete lookahead sets throughout the states */
propagate_all_lookaheads();
return start_state;
}
