Input/Output Language

           <sentence> ::= <judgment>
                        | <question>
                        | <goal>
           <judgment> ::= <statement> <truth-value>
           <question> ::= <statement>
               <goal> ::= <statement> <desire-value>
          <statement> ::= <<term> <relation> <term>>
                        | <compound-statement>
                        | <term>
               <term> ::= <word>
                        | <variable>
                        | <compound-term>
                        | <statement>
           <relation> ::= -->                              // inheritance
                        | <->                              // similarity
                        | {--                              // instance
                        | --]                              // property
                        | {-]                              // instance-property
                        | ==>                              // implication
                        | <=>                              // equivalence
                        | =/>                              // predictive implication
                        | =\>                              // retrospective implication
                        | </>                              // predictive equivalence
 <compound-statement> ::= (-- <statement>)                 // negation
                        | (&& <statement> <statement>+)    // conjunction
                        | (|| <statement> <statement>+)    // disjunction
                        | (&/ <statement> <statement>+)    // sequential conjunction
                        | (/> <statement>)                 // future tense
                        | (\> <statement>)                 // past tense
      <compound-term> ::= {<term>+}                        // extensional set
                        | [<term>+]                        // intensional set
                        | (& <term> <term>+)               // extensional intersection
                        | (| <term> <term>+)               // intensional intersection
                        | (- <term> <term>)                // extensional difference
                        | (~ <term> <term>)                // intensional difference
                        | (* <term> <term>+)               // product
                        | (/ <term> <term>)                // extensional image
                        | (\ <term> <term>)                // intensional image
           <variable> ::= <dependent-var>
                        | <independent-var>
                        | <query-var>
      <dependent-var> ::= #<word>(<independent-var>*)
    <independent-var> ::= #<word>
          <query-var> ::= ?<word>
        <truth-value> ::= %<frequency> <confidence>%
       <desire-value> ::= !<frequency> <confidence>!
          <frequency> : real number in [0, 1]
         <confidence> : real number in (0, 1), with 0.9 as default
               <word> : string in an alphabet

Graphical User Interface

• Main Window: it contains a menu bar, a text area, a clock field, and four command buttons.
• The following menu items are available in the applet version of NARS:
• Memory/[Initialize]: vacate the memory.
• View/[Concepts]: open a Bag Window to display all concepts.
• View/[Task Buffer]: open a Bag Window to display the new tasks to be processed.
• View/[Inference Log]: show the Inference Window.
• View/[Input Window]: show the Input Window.
• Parameter/[Task Forgetting Rate]: display the task forgetting rate, which controls how fast the priority values of tasks decay, in a Parameter Window.
• Parameter/[Belief Forgetting Rate]: display the belief forgetting rate, which controls how fast the priority values of beliefs decay, in a Parameter Window.
• Parameter/[Concept Forgetting Rate]: display the concept forgetting rate, which controls how fast the priority values of concepts decay, in a Parameter Window.
• Parameter/[Report Silence Level]: display the report silence level, which indicates the resource-budget threshold for derived tasks to be reported to the user, in a Parameter Window.
• Help/[Related Information]: display pointers to NARS related information in a Message Window.
• Help/[About NARS]: display version and copyright information of NARS in a Message Window.
• The text area displays the conversation between the user and the system.
• Lines preceded by ">>>" are input provided by the user.
• Lines preceded by "<<<" are output provided by the system.
• Lines consist of single integers record the number of inference steps between input/output events.
• The Clock field is a counter of inference steps after the last input/output event.
• The command buttons correspond to basic operations:
• "Run": to start the inference engine.
• "Walk": to let the inference engine work for one cycle.
• "Stop": to stop the inference engine.
• "Exit": to exit NARS.
• Input Window: it contains a text area and four command buttons.
• The text area allows the user to type or paste input lines, each of which may be
• a judgment, which is a statement with a frequency value and (optional) a confidence value.
• a question, a statement without truth value, and may contain query variable to be matched.
• a number, indicating the inference steps between input events.
• a blank line, indicating a pause in the input.
• The command buttons correspond to basic operations:
• "OK": to feed the current lines into the system.
• "Hold": to stop feeding the lines.
• "Clear": to clear the text field.
• "Hide": to hide the window.
• Inference Window: it contains a text area and three command buttons.
• The text area displays information in each inference step, including
• a step number.
• the concept selected in the step.
• the task selected in the step, if any.
• the belief selected in the step, if any.
• the new task(s) derived in the step, if any.
• The command buttons correspond to basic operations:
• "Play": to display the information..
• "Stop": to stop displaying.
• "Hide": to close the window.
• Bag Window: it contains a text area, a slider (optional), and three command buttons.
• The text area displays the items in the bag, according to their priority levels.
• The slider, if included, indicates and adjusts the priority threshold for items to be displayed.
• The command buttons correspond to basic operations:
• "Play": to display the information.
• "Stop": to stop displaying.
• "Close": to close the window.
• Parameter Window: it contains a slider and three command buttons.
• The slider indicates and adjusts the current parameter value.
• The command buttons correspond to basic operations:
• "Undo": to reset the parameter to its previously saved value.
• "Default": to reset the parameter to its default value.
• "Hide": to save the current value and hide the window.
• Message Window: it contains a text area and a bottom.
• The text area displays a message to the user.
• The "OK" button closes the window.

• Window color:
  • blue means the main window.
  • purple means a window that has only one instance in the system.
  • green means a window that may have more than one instance in the system.
• Text background color:
  • white means can be edited.
  • light-cyan means display only.