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Common Lisp implementation running on the JVM
/*
* peek_char.java
*
* Copyright (C) 2004-2005 Peter Graves
* $Id: peek_char.java 13461 2011-08-11 17:01:41Z ehuelsmann $
*
* 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 (at your option) 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.
*
* As a special exception, the copyright holders of this library give you
* permission to link this library with independent modules to produce an
* executable, regardless of the license terms of these independent
* modules, and to copy and distribute the resulting executable under
* terms of your choice, provided that you also meet, for each linked
* independent module, the terms and conditions of the license of that
* module. An independent module is a module which is not derived from
* or based on this library. If you modify this library, you may extend
* this exception to your version of the library, but you are not
* obligated to do so. If you do not wish to do so, delete this
* exception statement from your version.
*/
package org.armedbear.lisp;
import static org.armedbear.lisp.Lisp.*;
// ### peek-char
public final class peek_char extends Primitive
{
private peek_char()
{
super("peek-char",
"&optional peek-type input-stream eof-error-p eof-value recursive-p");
}
@Override
public LispObject execute(LispObject[] args)
{
int length = args.length;
if (length > 5)
error(new WrongNumberOfArgumentsException(this, -1, 5));
LispObject peekType = length > 0 ? args[0] : NIL;
Stream stream = length > 1 ? inSynonymOf(args[1]) : getStandardInput();
boolean eofError = length > 2 ? (args[2] != NIL) : true;
LispObject eofValue = length > 3 ? args[3] : NIL;
// recursive-p is ignored
// boolean recursive = length > 4 ? (args[4] != NIL) : false;
if (peekType == NIL) {
// "If PEEK-TYPE is not supplied or NIL, PEEK-CHAR returns the next
// character to be read from INPUT-STREAM, without actually
// removing it from INPUT-STREAM."
final Stream in;
if (stream instanceof EchoStream)
// "When INPUT-STREAM is an echo stream, characters that are
// only peeked at are not echoed." Read from the echo stream's
// input stream to bypass the echo.
in = ((EchoStream)stream).getInputStream();
else
in = stream;
final LispObject result = in.readChar(eofError, eofValue);
if (result instanceof LispCharacter)
in.unreadChar((LispCharacter)result);
return result;
}
if (peekType == T) {
// "If PEEK-TYPE is T, then PEEK-CHAR skips over whitespace[2]
// characters, but not comments, and then performs the peeking
// operation on the next character."
Readtable rt = currentReadtable();
while (true) {
LispObject result = stream.readChar(eofError, eofValue);
if (result instanceof LispCharacter) {
char c = ((LispCharacter)result).value;
if (!rt.isWhitespace(c)) {
stream.unreadChar((LispCharacter)result);
return result;
}
} else
return result;
}
}
if (peekType instanceof LispCharacter) {
// "If PEEK-TYPE is a character, then PEEK-CHAR skips over input
// characters until a character that is CHAR= to that character is
// found; that character is left in INPUT-STREAM."
char c = ((LispCharacter)peekType).value;
while (true) {
LispObject result = stream.readChar(eofError, eofValue);
if (result instanceof LispCharacter) {
if (((LispCharacter)result).value == c) {
stream.unreadChar((LispCharacter)result);
return result;
}
} else
return result;
}
}
return error(new SimpleError(String.valueOf(peekType) +
" is an illegal peek-type."));
}
private static final Primitive PEEK_CHAR = new peek_char();
}