Automata tools contains a parser for finite state machines (FSMs).

The API

Automata tools provides 4 named exports:

• FSM_parser - a class; builds FSM Objects given an array of lines (the code) and a filename.

• traverse - takes an FSM Object and a string; returns the ending state (FSM_node) when the string is run through the state machine.

• StateCircle - a react component for rendering state machines as SVGs

• toSVG - given an FSM, returns an SVG as a string (which is really just a rendered StateCircle).

The CLI

Automata tools can be installed globally to get access to its CLI - available as alang.

1$ npm i -g automata-tools

There is built-in help available.

Syntax

The syntax for describing a finite state machine is very simple. Below is an example of an FSM:

1a Machine which accepts even binary numbers (not including the empty string)
2
3=> read odd
4
5read odd:
6	0 => read even
7
8(read even):
9	1 => read odd

Lets go through the key points.

line 3 (=> read odd) defines the initial state for the machine - in this case, it is a state called "read odd"

read odd is defined two lines later, with read odd: - this is a state definition, as indicated by the : at the end of the line

Immediately below that is a transition definition (0 => read even); when the machine reads a 0, it will move to a new state, read even.

read even is defined below that, with (read even):

The brackets around the state name define this as an accepting state - read odd, which does not have bracket, is a rejecting state.

The first line is a comment - all lines are if they cannot be parsed as either a state definition (ending in :) or as a transition definition (containing =>).

leading and trailing white space does not matter - the transition definitions are tabbed in for readability. A transition definition applies to the most recently defined state.

Note however that within a state name, whitespace is treated just like any other character, so hello world and hello world (with 2 spaces) are not the same.