Jatha FAQ

How do I run Jatha?

  java -classpath jatha.jar org.jatha.Jatha

     or, if you don't want to use the GUI:

  java -classpath jatha.jar org.jatha.Jatha -nodisplay

How do I use Jatha from within another Java program?

    import org.jatha.Jatha;


    Jatha myLisp  = new Jatha(false, false);
    // Create a new symbol
    LispValue  symbol1  = myLisp.parse("FOO", LispParser.PRESERVE); // preserve case
    // Evaluate a form:
    try {
      String input  = "(* 5 10)";
      LispValue result = myLisp.eval(input);
      System.out.println(input + " = " + result);
    } catch (Exception e) {
     System.err.println("LISP Exception: " + e);

How do I use LISP expressions with variables from Java?

Any of the following will work in v2.7.1 and higher. All return the value 35: 1) System.out.println(lisp.eval("(let ((x 7)) (* 5 x)))")); // uses a local variable 2) System.out.println(lisp.eval("(progn (setq x 7) (* 5 x))")); // executes multiple statements 3) System.out.println(lisp.eval("(setq x 7)")); // creates a global variable System.out.println(lisp.eval("(* 5 x)")); // uses a global variable The eval method accepts an optional second parameter that is a list of global variables. However, the global variable list is difficult to construct. The examples here are easier to use.

How do I use the dynatype package?

The org.jatha.dynatype package provides a rich set of dynamically-typed objects that parallel the Common LISP type system.

The root class is an interface called LispValue that is implemented by StandardLispValue. All values in the system are instances of LispValue. Usually, you should declare variables of type LispValue rather than more specific types.

    import org.jatha.Jatha;
    import org.jatha.dynatype.*;

    Jatha lisp = new Jatha(false, false);

    LispValue foo1 = lisp.makeInteger(7);
    LispValue foo2 = lisp.makeSymbol("Hello");
    LispValue foo3 = lisp.makeReal(3.14159);
    LispValue foo4 = lisp.makeList(foo1, foo2, foo3);

    LispValue foo5 = foo4.car();
    LispValue foo6 = foo4.second();

    System.out.println(foo1);   // and so on.
Sometimes you will want to access the Java version of a value rather than the LISP version. Usually this happens in boolean expressions. To access these values, use the basic_ methods. Instead of:
  if (foo1.numberp() == lisp.T)


  if (foo4.length().greaterThan(lisp.makeInteger(5)) == lisp.T)
It is easier to say:
  if (foo1.basic_numberp())


  if (foo1.basic_length() > 5)

All Sequence types have iterators, so you can iterate over a LispValue that is a list by doing standard Java iteration:

  Iterator listIterator = foo4.iterator();
  while (listIterator.hasNext())
    LispValue value = (LispValue)listIterator.next();

Of course you can also write a while loop that steps through the list using car() and cdr() if you like.