Simulation
The simulation panel sits at the bottom of the screen. Toggle it with ⌘.. It has two tabs: Single (step-through one string) and Multi (batch test multiple strings). The panel is 192px tall on desktop and adapts to a compact mobile layout.
Single mode: controls
Type an input string in the input field and use these controls:
| Shortcut | Action |
|---|---|
| ⌘ Enter | Start simulation: compute epsilon closure of initial state and enter stepping mode |
| ⌘ ' | Step: consume one input symbol, compute next states via transition function + epsilon closure |
| ⇧⌘ Enter | Fast Run: instantly compute final accept/reject result without stepping |
| ⌘0 | Reset: clear simulation state, return to idle |
Single mode: visual feedback
→ The input tape visualization shows each character in a cell: consumed symbols are dimmed (sunken background), the current symbol is highlighted in yellow, and remaining symbols have a normal background
→ An empty input string shows "ε (empty string)" as a hint
→ Active states on the canvas are highlighted with a yellow border and a semi-transparent yellow fill during stepping
→ The active state labels are shown as pills in the right panel (e.g., "q0, q1, q3" for NFA)
→ The status indicator shows: IDLE (gray), STEPPING (yellow), ACCEPTED (green), or REJECTED (red)
→ Final result shows a colored banner: "✓ String accepted by the DFA" (green) or "✗ String rejected" (red)
→ If no initial state is set, simulation immediately rejects with a "NO INITIAL STATE" warning
→ The idle state shows useful info: mode, state count, alphabet set, and warnings for missing initial or accepting states
NFA simulation algorithm
For NFA mode (and generally for DFA too, since the same engine handles both), simulation uses a set-based approach:
- →Start: Compute the epsilon closure of the initial state. This is the initial set of active states.
- →Step: For the current input symbol, compute the set of states reachable from any active state via that symbol, then take the epsilon closure of the result.
- →Accept: After all input is consumed, if any active state is accepting, the string is accepted.
- →Reject: If the active state set ever becomes empty (no valid transitions), the string is immediately rejected.
The epsilon closure is computed using a stack-based DFS: start with the given states, and for each state, follow all ε-transitions and add newly discovered states to the closure.
Multi-run (batch testing)
Switch to the "Multi" tab to test multiple strings at once. Enter one string per line in the textarea (an empty line represents ε), then click RUN ALL. Each string is run through the full automaton simulation independently.
→ Results show ✓ ACCEPT (green) or ✗ REJECT (red) for each string
→ A summary shows pass count: e.g., "3/5 pass"
→ The textarea placeholder suggests the format: one string per line
→ On mobile, the multi-run view has a max height of 45vh to prevent it from covering the canvas
