/*
* xtc - The eXTensible Compiler
* Copyright (C) 2005-2007 Robert Grimm
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* version 2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
* USA.
*/
package xtc.parser;
import xtc.tree.Location;
import xtc.tree.Visitor;
import xtc.util.Runtime;
import xtc.type.AST;
/**
* Visitor to void ordered choices, repetitions, and options. This
* visitor voids ordered choices, repetitions, and options, if all
* expressions appearing in such an expression are either void
* nonterminals or explicitly voided. It requires that a grammar has
* been {@link Resolver resolved} into a single module, that text-only
* productions have been {@link TextTester marked} as such, and that
* all expressions have been {@link Simplifier simplified}.
*
* @author Robert Grimm
* @version $Revision: 1.15 $
*/
public class ElementVoider extends Visitor {
/** The runtime. */
protected final Runtime runtime;
/** The analyzer utility. */
protected final Analyzer analyzer;
/** The flag for the top-level element. */
protected boolean isTopLevel;
/** The flag for the last element. */
protected boolean isLastElement;
/** The flag for suppressing the insertion of voided elements. */
protected boolean suppressVoided;
/** The flag for potentially having a value. */
protected boolean hasValue;
/**
* Create a new element voider.
*
* @param runtime The runtime.
* @param analyzer The analyzer.
*/
public ElementVoider(Runtime runtime, Analyzer analyzer) {
this.runtime = runtime;
this.analyzer = analyzer;
}
/**
* Wrap the specified element in a voiding operator.
*
* @param el The element to wrap.
* @return The wrapped element.
*/
protected Element wrap(Element el) {
Element result = new VoidedElement(el);
Location loc = el.getLocation();
result.setLocation(loc);
if (runtime.test("optionVerbose")) {
System.err.println("[Voiding expression at " + loc.line + ":" +
loc.column + " in " + analyzer.current().qName + "]");
}
return result;
}
/** Visit the specified self-contained module. */
public void visit(Module m) {
// Initialize the per-grammar state.
analyzer.register(this);
analyzer.init(m);
// Process the productioins.
for (Production p : m.productions) analyzer.process(p);
}
/** Visit the specified full production. */
public void visit(FullProduction p) {
// Text-only and token-level productions are ignored.
if (p.getBooleanProperty(Properties.TEXT_ONLY) ||
p.getBooleanProperty(Properties.TOKEN)) {
return;
}
isTopLevel = true;
isLastElement = false;
suppressVoided = AST.isVoid(p.type);
hasValue = false;
p.choice = (OrderedChoice)dispatch(p.choice);
}
/** Visit the specified ordered choice. */
public Element visit(OrderedChoice c) {
boolean top = isTopLevel;
isTopLevel = false;
boolean last = isLastElement;
boolean value = hasValue;
if ((! top) && (! last)) {
hasValue = false;
}
final int size = c.alternatives.size();
for (int i=0; i<size; i++) {
isLastElement = top || last;
c.alternatives.set(i, (Sequence)dispatch(c.alternatives.get(i)));
}
isLastElement = false;
Element result = c;
if ((! top) && (! last)) {
if (hasValue) {
hasValue = true;
} else {
hasValue = value;
if (! suppressVoided) {
result = wrap(result);
}
}
}
return result;
}
/** Visit the specified quantification. */
public Element visit(Quantification q) {
isTopLevel = false;
isLastElement = true;
boolean value = hasValue;
hasValue = false;
q.element = (Element)dispatch(q.element);
isLastElement = false;
Element result = q;
if (hasValue) {
hasValue = true;
} else {
hasValue = value;
if (! suppressVoided) {
result = wrap(result);
}
}
return result;
}
/** Visit the specified sequence. */
public Element visit(Sequence s) {
isTopLevel = false;
boolean last = isLastElement;
final int size = s.size();
for (int i=0; i<size; i++) {
isLastElement = last && (i == size-1);
s.elements.set(i, (Element)dispatch(s.get(i)));
}
isLastElement = false;
return s;
}
/** Visit the specified predicate. */
public Element visit(Predicate p) {
isTopLevel = false;
isLastElement = true;
boolean value = hasValue;
hasValue = false;
boolean suppress = suppressVoided;
suppressVoided = true;
p.element = (Element)dispatch(p.element);
isLastElement = false;
hasValue = value;
suppressVoided = suppress;
return p;
}
/** Visit the specified voided element. */
public VoidedElement visit(VoidedElement v) {
isTopLevel = false;
isLastElement = true;
boolean value = hasValue;
hasValue = false;
boolean suppress = suppressVoided;
suppressVoided = true;
v.element = (Element)dispatch(v.element);
isLastElement = false;
hasValue = value;
suppressVoided = suppress;
return v;
}
/** Visit the specified binding. */
public Binding visit(Binding b) {
isTopLevel = false;
isLastElement = true;
hasValue = false;
boolean suppress = suppressVoided;
suppressVoided = false;
b.element = (Element)dispatch(b.element);
if (b.element instanceof VoidedElement) {
runtime.error("binding for expression without value", b);
}
isLastElement = false;
hasValue = true;
suppressVoided = suppress;
return b;
}
/** Visit the specified string match. */
public StringMatch visit(StringMatch m) {
isTopLevel = false;
isLastElement = true;
hasValue = false;
boolean suppress = suppressVoided;
suppressVoided = false;
m.element = (Element)dispatch(m.element);
if (m.element instanceof VoidedElement) {
runtime.error("match for expression without value", m);
}
isLastElement = false;
hasValue = true;
suppressVoided = suppress;
return m;
}
/** Visit the specified parser action. */
public ParserAction visit(ParserAction pa) {
isTopLevel = false;
isLastElement = false;
hasValue = true;
return pa;
}
/** Visit the specified action. */
public Action visit(Action a) {
isTopLevel = false;
isLastElement = false;
if (a.setsValue()) {
hasValue = true;
}
return a;
}
/** Visit the specified nonterminal. */
public NonTerminal visit(NonTerminal nt) {
isTopLevel = false;
isLastElement = false;
FullProduction p = analyzer.lookup(nt);
if (! AST.isVoid(p.type)) {
hasValue = true;
}
return nt;
}
/**
* Visit the specified element. This method provides the default
* implementation for terminals, parse tree nodes, null literals,
* node markers, and value elements.
*/
public Element visit(Element e) {
isTopLevel = false;
isLastElement = false;
hasValue = true;
return e;
}
}