User:EMBee/Scrap: Difference between revisions

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* add "suggest task" and "task by category" links to tasks page.
this code is based on [http://jfkbits.blogspot.com/2008/05/thoughts-on-s-expression-parser.html] and [http://jfkbits.blogspot.com/2008/05/thoughts-on-s-expression-lexer.html]
* suggest task for binary math.
it is available under the GPL. the author has expressed permission to publish his code here, but has not yet confirmed that using the GNU FDL is ok. once i receive this confirmation i will add the code to [[S-Expressions]]
* draft task for math with boolean lists like in early lisp as per http://paste.lisp.org/display/126287

: You should give the name of the original author. Giving a URL is not enough while the content at the given URL may disappear.

LispParser.java:
<lang Java>package jfkbits;

import java.util.Enumeration;
import java.util.Iterator;
import java.util.Vector;


public class LispParser
{
LispTokenizer tokenizer;
public LispParser(LispTokenizer input)
{
tokenizer=input;
}

public class ParseException extends Exception
{

}

public interface Expr
{
// abstract parent for Atom and ExprList
}
public class ExprList extends Vector implements Expr
{
public String toString()
{
String output = "(";
for(Enumeration it=this.elements(); it.hasMoreElements(); )
{
Expr expr = (Expr) it.nextElement();
output += expr.toString();
if (it.hasMoreElements())
output += " ";
}
output += ")";
return output;
}
public ExprList(AbstractCollection exprs)
{
super(exprs);
}

public ExprList()
{
super();
}

}
public class Atom implements Expr
{
String name;
public String toString()
{
return name;
}
public Atom(String text)
{
name = text;
}

}
public Expr parseExpr() throws ParseException
{
Token token = tokenizer.nextToken();
Expr retval = (token.type == '(')?
parseExprList(token)
: new Atom(token.text);
return retval;
}


protected Expr parseExprList(Token openParen) throws ParseException
{
ExprList acc = new ExprList();
while(tokenizer.peekToken().type != ')')
{
Expr element = parseExpr();
acc.add(element);
}
Token closeParen = tokenizer.nextToken();
return acc;
}

}
</lang>

LispTokenizer.java:
<lang java>
package jfkbits;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.io.StreamTokenizer;
import java.io.StringReader;
import java.util.Iterator;

public class LispTokenizer implements Iterator
{
// Instance variables have default access to allow unit tests access.
StreamTokenizer m_tokenizer;
IOException m_ioexn;

/** Constructs a tokenizer that scans input from the given string.
* @param src A string containing S-expressions.
*/
public LispTokenizer(String src)
{
this(new StringReader(src));
}

/** Constructs a tokenizer that scans input from the given Reader.
* @param r Reader for the character input source
*/
public LispTokenizer(Reader r)
{
if(r == null)
r = new StringReader("");
BufferedReader buffrdr = new BufferedReader(r);
m_tokenizer = new StreamTokenizer(buffrdr);
m_tokenizer.resetSyntax(); // We don't like the default settings

m_tokenizer.whitespaceChars(0, ' ');
m_tokenizer.wordChars(' '+1,255);
m_tokenizer.ordinaryChar('(');
m_tokenizer.ordinaryChar(')');
m_tokenizer.ordinaryChar('\'');
m_tokenizer.commentChar(';');
m_tokenizer.quoteChar('"');
}

public Token peekToken()
{
if(m_ioexn != null)
return null;
try
{
m_tokenizer.nextToken();
}
catch(IOException e)
{
m_ioexn = e;
return null;
}
if(m_tokenizer.ttype == StreamTokenizer.TT_EOF)
return null;
Token token = new Token(m_tokenizer);
m_tokenizer.pushBack();
return token;
}
public boolean hasNext()
{
if(m_ioexn != null)
return false;
try
{
m_tokenizer.nextToken();
}
catch(IOException e)
{
m_ioexn = e;
return false;
}
if(m_tokenizer.ttype == StreamTokenizer.TT_EOF)
return false;
m_tokenizer.pushBack();
return true;
}

/** Return the most recently caught IOException, if any,
*
* @return
*/
public IOException getIOException()
{
return m_ioexn;
}

public Token nextToken()
{
return (Token)next();
}

public Object next()
{
try
{
m_tokenizer.nextToken();
}
catch(IOException e)
{
m_ioexn = e;
return null;
}

Token token = new Token(m_tokenizer);
return token;
}

public void remove()
{
}
}
</lang>

{{Lines_too_long|Java}}

SexprDemo.java:
<lang Java>
import java.io.IOException;
import java.util.AbstractCollection;

import jfkbits.LispParser;
import jfkbits.LispParser.Expr;
import jfkbits.LispParser.ExprList;
import jfkbits.LispParser.ParseException;
import jfkbits.LispTokenizer;
import jfkbits.Token;

public class SexprDemo
{
public static void main(String args[])
throws IOException
{

LispTokenizer tzr = new LispTokenizer("((data \"quoted data\" 123 4.5) (data (!@# (4.5) \"(more\" \"data)\")))");
LispParser parser = new LispParser(tzr);
ExprList result = null;
Enumeration output = null;
try
{
result = (ExprList) parser.parseExpr();
System.out.println(result.toString());
}
catch (ParseException e1)
{
// TODO Auto-generated catch block
e1.printStackTrace();
}

}
}
</lang>

Latest revision as of 10:59, 5 January 2012

  • add "suggest task" and "task by category" links to tasks page.
  • suggest task for binary math.
  • draft task for math with boolean lists like in early lisp as per http://paste.lisp.org/display/126287
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