Package java_cup.runtime
Class virtual_parse_stack
java.lang.Object
java_cup.runtime.virtual_parse_stack
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.
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Field Summary
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Constructor Summary
ConstructorsConstructorDescriptionvirtual_parse_stack
(Stack shadowing_stack) Constructor to build a virtual stack out of a real stack. -
Method Summary
Modifier and TypeMethodDescriptionboolean
empty()
Indicate whether the stack is empty.protected void
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).
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Field Details
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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_nextTop 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
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.
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Constructor Details
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virtual_parse_stack
Constructor to build a virtual stack out of a real stack.- Throws:
Exception
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Method Details
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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
Return value on the top of the stack (without popping it).- Throws:
Exception
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pop
Pop the stack.- Throws:
Exception
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push
public void push(int state_num) Push a state number onto the stack.
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