fsm

This module implements a Finite State Machine (FSM). The FSM is composed of states and transitions between them. These need to be specified by the client.

Usage

Have a look at fsm_test.v for usage examples.

On each run(), all the possible transitions from the current state are evaluated. The first transition for the current state, whose condition evaluates to true is taken (the condition is specified by a transition callback function).

In a successful transition, the current state changes to the new one. When that happens:* the client-specified on_exit() handler from the current state is called.

• the client-specified on_entry() handler of the new state is called.

After all transitions are checked, and thus the state is changed, the client-specified on_run() handler of the now current state is called.

Plot States and Transitions

This module includes a tool for generating dot diagrams from .v source code, that defines a FSM. The tool is located in fsm_graph.v.

Here is an example of how to generate a .dot file with the graph and transitions:

v run vlib/datatypes/fsm/tools/fsm_graph.v -f vlib/datatypes/fsm/fsm_test.v > graph.dot

You can convert the generated .dot file to a PNG file with Graphviz's dot conversion tool:

v run vlib/datatypes/fsm/tools/fsm_graph.v -f vlib/datatypes/fsm/fsm_test.v > graph.dot
dot -Tpng graph.dot > graph.png
xdg-open graph.png

You can also visualise it with Graphviz (the dot command) & ImageMagick (the display command):

v run vlib/datatypes/fsm/tools/fsm_graph.v -f vlib/datatypes/fsm/fsm_test.v | dot -Tpng | display

To view the .dot file, you can also use any of the Graphviz Graphical Interfaces and xdot in particular:

v run vlib/datatypes/fsm/tools/fsm_graph.v -f vlib/datatypes/fsm/fsm_test.v | xdot -

In all of the above examples, you can replace vlib/datatypes/fsm/fsm_test.v with the path to your own .v code that imports and uses fsm.

fn new() StateMachine

StateMachine static method returns a new StateMachine instance.

type ConditionFn = fn (receiver voidptr, from string, to string) bool

type EventHandlerFn = fn (receiver voidptr, from string, to string)

struct StateMachine {
mut:
	states        map[string]State
	transitions   map[string][]Transition
	current_state string
}

fn (mut s StateMachine) set_state(name string) !

set_state sets the current state of the state machine to the given state by name.

fn (mut s StateMachine) get_state() string

get_state returns the current state of the state machine.

fn (mut s StateMachine) add_state(name string, entry EventHandlerFn, run EventHandlerFn, exit EventHandlerFn)

add_state adds a new state to the state machine. It takes the name of the state, and three event handlers: entry, run, and exit.

fn (mut s StateMachine) add_transition(from string, to string, condition_handler ConditionFn)

add_transition adds a new transition to the state machine. It takes the from and to states, and a condition handler.

fn (mut s StateMachine) run(receiver voidptr) !

run runs the state machine. It takes a receiver argument that is passed to the event handlers.