tolist.java

SRI international 发布的OAA框架软件

package com.sri.oaa2.icl;

/**
 * Objects of this class convert IclTerms to an IclList.  Currently only
 * does the conversion if IclTerm.isList() returns true for the term.
 */
public final class ToList implements OaaPrologVisitor
{
  /// Our singleton instance
  private static final ToList singleton = new ToList();

  protected ToList() 
  {
  }

  public final Object visit(IclTerm node, Object data) 
  {
    return null;
  }
  
  public final Object visit(IclStruct node, Object data) 
  {
    return null;
  }
  
  public final Object visit(IclList node, Object data) 
  {
    return node;
  }
  
  public final Object visit(IclGroup node, Object data) 
  {
    return null;
  }
  
  public final Object visit(IclInt node, Object data) 
  {
    return null;
  }
  
  public final Object visit(IclFloat node, Object data) 
  {
    return null;
  }
  
  public final Object visit(IclStr node, Object data) 
  {
    return null;
  }
  
  public final Object visit(IclVar node, Object data) 
  {
    return null;
  }
  
  /**
   * Get an instance of a ToList object.  This avoids multiple calls to the constructor.
   * ToList is thread safe.
   */
  public final static ToList getInstance() 
  {
    return singleton;
  }

  /**
   * Convert an IclTerm to an IclList, if possible.  If not, return the given default.
   *
   * @param IclTerm t: the term to convert
   * @param IclList def: the default to use
   * @return IclList: the IclTerm as an IclList, or the default value
   */
  public final IclList from(IclTerm t, IclList def) 
  {
    if(t.isList()) {
      return (IclList)t;
    }
    
    IclList l = (IclList)t.accept(this, null);
    if(l == null) {
      return def;
    }
    return l;
  }

  /**
   * Convert an IclTerm to an IclList, if possible.  If not, throw an UnsupportedOperationException.
   *
   * @param IclTerm t: the term to convert
   * @return IclList: the term as an IclList
   * @throws UnsupportedOperationException if no such conversion possible
   */
  public final IclList from(IclTerm t) throws UnsupportedOperationException
  {
    if(t.isList()) {
      return (IclList)t;
    }
    
    IclList l = (IclList)t.accept(this, null);
    if(l == null) {
      throw new UnsupportedOperationException("ToList not supported by " + OaaPrologParser._tokenNames[t.getType()]);
    }
    return l;
  }  
}