code: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements. See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership. The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the  "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  /*
   * $Id$
   */
  
  package org.apache.xalan.xsltc.compiler;
  
  import java.util.Vector;
  
  import org.apache.bcel.generic.BranchHandle;
  import org.apache.bcel.generic.ConstantPoolGen;
  import org.apache.bcel.generic.GOTO_W;
  import org.apache.bcel.generic.IFEQ;
  import org.apache.bcel.generic.InstructionHandle;
  import org.apache.bcel.generic.InstructionList;
  import org.apache.xalan.xsltc.compiler.util.BooleanType;
  import org.apache.xalan.xsltc.compiler.util.ClassGenerator;
  import org.apache.xalan.xsltc.compiler.util.ErrorMsg;
  import org.apache.xalan.xsltc.compiler.util.MethodGenerator;
  import org.apache.xalan.xsltc.compiler.util.MethodType;
  import org.apache.xalan.xsltc.compiler.util.NodeSetType;
  import org.apache.xalan.xsltc.compiler.util.Type;
  import org.apache.xalan.xsltc.compiler.util.TypeCheckError;
  
  /**
   * @author Jacek Ambroziak
   * @author Santiago Pericas-Geertsen
   * @author Morten Jorgensen
   * @author Erwin Bolwidt <ejb@klomp.org>
   */
  abstract class Expression extends SyntaxTreeNode {
      /**
       * The type of this expression. It is set after calling 
       * <code>typeCheck()</code>.
       */
      protected Type _type;
  
      /**
       * Instruction handles that comprise the true list.
       */
      protected FlowList _trueList = new FlowList();
  
      /**
       * Instruction handles that comprise the false list.
       */
      protected FlowList _falseList = new FlowList();
  
      public Type getType() {
  	return _type;
      }
  
      public abstract String toString();
  
      public boolean hasPositionCall() {
  	return false;		// default should be 'false' for StepPattern
      }
  
      public boolean hasLastCall() {
  	return false;
      }
  		
      /**
       * Returns an object representing the compile-time evaluation 
       * of an expression. We are only using this for function-available
       * and element-available at this time.
       */
      public Object evaluateAtCompileTime() {
  	return null;
      }
  
      /**
       * Type check all the children of this node.
       */
      public Type typeCheck(SymbolTable stable) throws TypeCheckError {
  	return typeCheckContents(stable);
      }
  
      /**
       * Translate this node into JVM bytecodes.
       */
      public void translate(ClassGenerator classGen, MethodGenerator methodGen) {
  	ErrorMsg msg = new ErrorMsg(ErrorMsg.NOT_IMPLEMENTED_ERR,
  				    getClass(), this);
  	getParser().reportError(FATAL, msg);
      }
  	
      /**
       * Translate this node into a fresh instruction list.
       * The original instruction list is saved and restored.
       */
      public final InstructionList compile(ClassGenerator classGen,
  					 MethodGenerator methodGen) {
  	final InstructionList result, save = methodGen.getInstructionList();
  	methodGen.setInstructionList(result = new InstructionList());
  	translate(classGen, methodGen);
  	methodGen.setInstructionList(save);
  	return result;
      }
  
      /**
       * Redefined by expressions of type boolean that use flow lists.
       */
      public void translateDesynthesized(ClassGenerator classGen,
  				       MethodGenerator methodGen) {
  	translate(classGen, methodGen);
  	if (_type instanceof BooleanType) {
  	    desynthesize(classGen, methodGen);
  	}
      }
  
      /**
       * If this expression is of type node-set and it is not a variable
       * reference, then call setStartNode() passing the context node.
       */
      public void startIterator(ClassGenerator classGen,
  				   MethodGenerator methodGen) {
  	// Ignore if type is not node-set
  	if (_type instanceof NodeSetType == false) {
  	    return;
  	}
  
  	// setStartNode() should not be called if expr is a variable ref
  	Expression expr = this;
  	if (expr instanceof CastExpr) {
  	    expr = ((CastExpr) expr).getExpr();
  	}
  	if (expr instanceof VariableRefBase == false) {
  	    final InstructionList il = methodGen.getInstructionList();
  	    il.append(methodGen.loadContextNode());
  	    il.append(methodGen.setStartNode());
  	}
      }
  
      /**
       * Synthesize a boolean expression, i.e., either push a 0 or 1 onto the 
       * operand stack for the next statement to succeed. Returns the handle
       * of the instruction to be backpatched.
       */
      public void synthesize(ClassGenerator classGen, MethodGenerator methodGen) {
  	final ConstantPoolGen cpg = classGen.getConstantPool();
  	final InstructionList il = methodGen.getInstructionList();
  	_trueList.backPatch(il.append(ICONST_1));
  	final BranchHandle truec = il.append(new GOTO_W(null));
  	_falseList.backPatch(il.append(ICONST_0));
  	truec.setTarget(il.append(NOP));
      }
  
      public void desynthesize(ClassGenerator classGen,
  			     MethodGenerator methodGen) {
  	final InstructionList il = methodGen.getInstructionList();
  	_falseList.add(il.append(new IFEQ(null)));
      }
  
      public FlowList getFalseList() {
  	return _falseList;
      }
  
      public FlowList getTrueList() {
  	return _trueList;
      }
  
      public void backPatchFalseList(InstructionHandle ih) {
  	_falseList.backPatch(ih);
      }
  
      public void backPatchTrueList(InstructionHandle ih) {
  	_trueList.backPatch(ih);
      }
  
      /**
       * Search for a primop in the symbol table that matches the method type 
       * <code>ctype</code>. Two methods match if they have the same arity.
       * If a primop is overloaded then the "closest match" is returned. The
       * first entry in the vector of primops that has the right arity is 
       * considered to be the default one.
       */
      public MethodType lookupPrimop(SymbolTable stable, String op,
  				   MethodType ctype) {
  	MethodType result = null;
  	final Vector primop = stable.lookupPrimop(op);
  	if (primop != null) {
  	    final int n = primop.size();
  	    int minDistance = Integer.MAX_VALUE;
  	    for (int i = 0; i < n; i++) {
  		final MethodType ptype = (MethodType) primop.elementAt(i);
  		// Skip if different arity
  		if (ptype.argsCount() != ctype.argsCount()) {
  		    continue;
  		}
  				
  		// The first method with the right arity is the default
  		if (result == null) {
  		    result = ptype;		// default method
  		}
  
  		// Check if better than last one found
  		final int distance = ctype.distanceTo(ptype);
  		if (distance < minDistance) {
  		    minDistance = distance;
  		    result = ptype;
  		}
  	    }		
  	}	
  	return result;
      }	
  }
  