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  package jason.stdlib;

Internal action: .puts.

Description: used for printing messages to the console where the system is running, or unifying the message to a variable parameter. It receives one string parameter, containing escaped variable names that are replaced by their bindings in the current intention's unifier. Terms are made ground according to the current unifying function before being printed out. No new line is printed after the parameters. In this version a user can also include any Jason expression (logical or arithmetic) that will be replaced by it's evaluated value.

The precise format and output device of the message is defined by the Java logging configuration as defined in the file in the project directory.


  • +message (string): the string to be printed out.
  • -output (any variable [optional]): the variable to print the processed result.


  • .puts("Testing variable #{A}"): prints out to the console the supplied string replacing #{A} with the value of variable A.
  • .puts("Testing variable #{A}, into B", B): tries to unify B with the supplied string replacing #{A} with the value of variable A.
  • .puts("The value of the expression is #{X+2}"): prints out the result of the X+2 expression. Assuming X is unified to a numeric value, the printed result will be the sum of X and two, if X is unified to any other value, the original expression (X+2) will be printed.

Felipe Meneguzzi (
 public class puts extends DefaultInternalAction {
     private static final long serialVersionUID = 1L;
     private static InternalAction singleton = null;
     public static InternalAction create() {
         if ( == null)
              = new puts();
         return ;
     //Pattern regex = Pattern.compile("#\\{\\p{Upper}\\p{Alnum}*\\}");
     Pattern regex = Pattern.compile("#\\{\\p{Alnum}+\\}");
     public Object execute(TransitionSystem tsUnifier unTerm[] args)
             throws Exception {
         if (!args[0].isString()) {
             return false;
         StringBuffer sb = new StringBuffer();
         for (Term term : args) {
             if (!term.isString()) {
             StringTerm st = (StringTermterm;
             Matcher matcher = .matcher(st.getString());
             while (matcher.find()) {
                  * System.out.println("I found the text \"" "\"
                  * starting at index "+matcher.start()+ " and ending at index
                  * "+matcher.end());
                 String sVar =;
                sVar = sVar.substring(2, sVar.length() - 1);
                try {
                    Term t = ASSyntax.parseTerm(sVar);
                    //We use t.apply to evaluate any logical or arithmetic expression in Jason
                } catch (ParseException pe) {
                    // TODO: handle exception
                    // TODO: Decide whether or not we should ignore the exception and print the call instead
                    // Right now, if I get a parse error from ASSyntax, I just print the original escaped
                    // sequence, so a user can see that his/her expression was problematic
        if (args[args.length - 1].isVar()) {
            StringTerm stRes = new StringTermImpl(sb.toString());
            return un.unifies(stResargs[args.length - 1]);
        } else {
            return true;
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