java_cup.runtime
Class virtual_parse_stack
java.lang.Object
java_cup.runtime.virtual_parse_stack
public class virtual_parse_stack
extends java.lang.Object
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.
Version:
- Frank Flannery
lr_parser
protected int | real_next - Top of stack indicator for where we leave off in the real stack.
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protected Stack | real_stack - The real stack that we shadow.
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protected Stack | vstack - The virtual top portion of the stack.
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virtual_parse_stack(Stack shadowing_stack) - Constructor to build a virtual stack out of a real stack.
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boolean | empty() - Indicate whether the stack is empty.
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protected void | get_from_real() - Transfer an element from the real to the virtual stack.
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void | pop() - Pop the stack.
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void | push(int state_num) - Push a state number onto the stack.
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int | top() - Return value on the top of the stack (without popping it).
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real_next
protected int real_next
Top 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.
real_stack
protected Stack 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.
vstack
protected 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.
virtual_parse_stack
public virtual_parse_stack(Stack shadowing_stack)
throws java.lang.Exception
Constructor to build a virtual stack out of a real stack.
empty
public boolean empty()
Indicate whether the stack is empty.
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.
pop
public void pop()
throws java.lang.Exception
Pop the stack.
push
public void push(int state_num)
Push a state number onto the stack.
top
public int top()
throws java.lang.Exception
Return value on the top of the stack (without popping it).