Automata tools contains a parser for finite state machines (FSMs).
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).
Automata tools can be installed globally to get access to its CLI - available as alang.
$ npm i -g automata-toolsThere is built-in help available.
The syntax for describing a finite state machine is very simple. Below is an example of an FSM:
a Machine which accepts even binary numbers (not including the empty string)
=> read odd
read odd:
0 => read even
(read even):
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.