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BackQuoteSubstitute.java

/* {{{ License.
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or any later version.
 *
 * 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, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */ //}}}

// :indentSize=4:lineSeparator=\n:noTabs=false:tabSize=4:folding=explicit:collapseFolds=0:

package org.mathpiper.lisp.behaviours;

import org.mathpiper.lisp.cons.Cons;
import org.mathpiper.lisp.Utility;
import org.mathpiper.lisp.cons.ConsPointer;
import org.mathpiper.lisp.Environment;
import org.mathpiper.lisp.cons.SublistCons;

/** Substitute behaviour for backquote mechanism as in LISP.
 * When typing `(...) all occurrences of @a will be
 * replaced with:
 * 1) a evaluated if a is an atom
 * 2) function call with function name replaced by evaluated
 *    head of function if a is a function. For instance, if
 *    a is f(x) and f is g, then f(x) gets replaced by g(x)
 */
00035 public class BackQuoteSubstitute implements Substitute
{
      Environment iEnvironment;

      public BackQuoteSubstitute(Environment aEnvironment)
      {
            iEnvironment = aEnvironment;
      }
      public boolean matches(Environment aEnvironment,ConsPointer aResult, ConsPointer aElement) throws Exception
      {
            if (! (aElement.car() instanceof ConsPointer)) return false;

            Cons ptr = ((ConsPointer) aElement.car()).getCons();
            if (ptr == null) return false;

            if (!( ptr.car() instanceof String)) return false;

            if (ptr.car().equals("`"))
            {
                  aResult.setCons(aElement.getCons());
                  return true;
            }

            if (!ptr.car().equals("@"))
                  return false;

            ptr = ptr.cdr().getCons();

            if (ptr == null)
                  return false;

            if (ptr.car() instanceof String)
            {
                  ConsPointer cur = new ConsPointer();
                  cur.setCons(ptr);
                  iEnvironment.iLispExpressionEvaluator.evaluate(iEnvironment, aResult, cur);
                  return true;
            }
            else
            {
                  ptr = ((ConsPointer) ptr.car()).getCons();
                  ConsPointer cur = new ConsPointer();
                  cur.setCons(ptr);
                  ConsPointer args = new ConsPointer();
                  args.setCons(ptr.cdr().getCons());
                  ConsPointer result = new ConsPointer();
                  iEnvironment.iLispExpressionEvaluator.evaluate(iEnvironment, result, cur);
                  result.cdr().setCons(args.getCons());
                  ConsPointer result2 = new ConsPointer();
                  result2.setCons(SublistCons.getInstance(aEnvironment,result.getCons()));
                  Utility.substitute(aEnvironment, aResult,result2, this);
                  return true;
            }
            //      return false;
      }

};

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