mova

mova

mova is a small domain-specific language (DSL) for defining state machines with states, triggers, and actions. It is designed to be declarative, readable, and extensible, and serves as a simple way to express event-driven behavior in a static configuration file.

Overview

A mova file (.mova) describes one or more states, each with optional initial actions and triggers. A trigger listens for an event and can execute actions or move to another state.

The language supports:

• constants via key = value;
• states via state name { ... };
• actions (function calls with arguments)
• state transitions via move <state>
• event-data via on EVENT(x=..., y=...) -> ACTIONS;

Syntax

1. Constants

press = 1;
release = 0;

Constants are variables and can later be used as action arguments or event-data. Supported types: integers, floats, strings, booleans.

2. States

Each state defines optional init actions and one or more triggers.

state init {
    set_led(led1=1, led2=0, led3=0, led4=0);
    on A(event=press) -> KEY_A, KEY_B;
    on B(event=press) -> move cursor;
};

• state init { ... }; defines a named state.
• The init section (before any on) runs when entering the state.
• on EVENT(...) -> ...; defines a trigger and its reactions.

3. Triggers

Triggers react to incoming events. Each trigger may define one or more event-data fields that must match the trigger’s spec.

on ACCEL(x, y, z) -> MOUSE_MOVE(x, y, z);

• Left side (x, y, z) = event-data received from an Emit() call.
• Right side = one or more actions, separated by commas.
• Each action can have arguments.

4. Actions

Actions refer to functions defined in the registry (e.g. KEY_A, MOUSE_MOVE, etc.). Arguments are evaluated as variables (constants or event-data).

MOUSE_MOVE(x=x, y=y, z=z);
set_led(led1=1, led2=0, led3=0, led4=0);

5. State Transitions

A transition moves execution to another state:

move cursor;

When executed, cursor becomes the active state. Its init actions will run automatically.

Full Example

# Wiimote mapping example

press   = 1;
release = 0;

state init {
    set_led(led1=1, led2=0, led3=0, led4=0);
    on A(event=press)   -> KEY_A, KEY_B;
    on B(event=press)   -> move cursor;
};

state cursor {
    set_led(led1=0, led2=1, led3=0, led4=0);
    on ACCEL(x, y, z)   -> MOUSE_MOVE(x, y, z);
    on A(event=press)   -> MOUSE_LEFT(event=press);
    on B(event=press)   -> move init;
};

Type Checking and Error Messages

mova enforces type consistency between constants, event-data, and actions.

Terminology is consistent across all errors:

• unspecified → not declared in the spec
• event-data → arguments passed to Emit
• argument → parameters of an action call
• variable → either a constant or event-data

Interpreter Architecture

The reference implementation consists of:

File Extension

.mova (Alternative suggestions: .mach, .trig — depending on final project name.)

Design Goals

• Minimal syntax, easy to read and parse
• Consistent, precise error reporting
• Embeddable in Go programs
• Plan 9-inspired simplicity — no runtime magic, just parsing and execution

License

Zlib