The Automaton Editor

Editing a finite state automaton.

The Editor Pane

The editor pane has two main components. On the top is a detachable tool bar (the section with the four iconic buttons), and on the bottom is the canvas where the automaton is drawn.

The automaton is edited through clicks on the canvas. The current action taken in response to those clicks depends on the currently selected tool. Notice in the picture that the icon that looks like a fat arrow is darker: this indicates that it is selected.

To select another tool, click on it, or use its shortcut key. You can get the shortcut key, as well as a short description of the tool, by holding the cursor over the tool button. After a short time this should display a tool-tip with information.

The descriptions for those tools is shown below.

The Tools

The State Tool (the "S" key)

While the state tool is selected, a click on the canvas will create a new state centered at the point that was clicked.

The Transition Tool (the "T" key)

By dragging from one state to another, a transition from the first state clicked to the second state dragged to will be created. Looping transitions from a state to itself are handled no differently. Once two states are joined with the tool, the user will then be asked for certain parameters of the transitions.

The Delete Tool (the "D" key)

This will erase any transition or state it is clicked on. If a state is deleted, those transitions incident on or emanating from a state will be deleted as well.

The Attribute Tool (the "A" key)

This tool is used to modify existing states and transitions. To move states, drag them with this tool. Dragging transitions will move transitions. Clicking on a transition edits a transition. A user may right-click (control click on Macs that have only one mouse button) on a state to bring up a pop-up menu to define the state as final, to define the state as initial, to set its label (an auxiliary description for a state), to clear its label (if it has one), or to clear all labels of all states.

Editing Transitions

Only one transition may be edited at a time. While a transition is being edited, fields appear that allow the user to change parameters regarding that particular transition. Each field corresponds to a particular parameter of that transition. In order to find out which is which during runtime, hold the mouse cursor over one of the fields; a tool tip will pop up to tell what it is.

Editing a Turing machine transition.

A finite state automaton's transition editor will have a single field representing what characters are read from the input. A pushdown automaton's transition editor will have three fields, the first to define what characters to read from input, the second to define what characters to pop from the stack, and the third to define what characters to push. A Turing machine's transition editor will also have three fields, one for the read character, one for the write character, and one for the direction to move the tape head (L, S, and R for left, stay, and right). A two-tape Turing machine is similar, but it has two rows; each row follows the convention of Turing machine transitions defined previously. To enter lambda entries, simply leave a field blank. Leaving a field blank in a Turing machine is not lambda, but is the blank tape symbol (represented as a square).

To stop editing, take some other action with the tool or click in an empty space on the canvas. If there is anything irregular about the transition entered, the program will display an error and revert the transition to its state before the edit. Currently, the only restriction on transitions are on transitions for Turing machine; a Turing machine transition must read exactly one character and write exactly one character per tape. If the read or write fields for a Turing machine are left empty, the blank tape alphabet symbol is assumed to be the content of that field.

In Haiku

In the editor,
The canvas dominates all,
The tool-bar's on top.

Choose a different tool.
Your clicks upon the canvas
now serve different ends.

Clicks on the canvas
make new automaton states
when this tool's active.

This creates transitions.
From one state to another
one may drag the mouse.

A table pops up
to define the transition.
When done, click elsewhere.

State or transitions
are removed from the canvas
through use of this tool.

This changes attributes.
A click edits transitions,
dragging states moves states.

Right click on a state.
A menu lets you make it
final or initial.

To switch tools quickly
without much mousing about
use the shortcut keys.

Tools each have tool-tips.
Mouse over a tool to see it.
The shortcut's shown there.

When you are finished,
to apply an operation,
choose from the menu.