I used Kotlin and Antlr to make a state machine compiler

Makina

Makina is a hierarchical state machine source-to-source translator. It takes state machine descriptions as input and produces C language implementations of those state machines.
Demo
Syntax

Each file given as input to the Makina compiler represents a single state machine. At the top of the file the name of the machine is specified with a machine statement:
Machines

machine Oven;

Here the machine is called Oven.
States

States are defined below that with state definitions:

machine Oven;
state closed {
    
}

Now the state machine Oven has one state called closed.

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Of course state machines usually have more than one state. As many states as are required can be added to a single machine:

machine Oven;
state closed {
    
}
state open {
    
}

Now Oven has two states: closed and open.
Event Handlers

In addition to states, state machines also define events. Events are triggers that cause the state machine to take action. In order to assign an action to an event a state must include an event handler that could look like this:

machine Oven;
state closed {
    on open -> open;
}
state open {
    
}

The state closed now has an handler for the event named open. The handler causes the machine Oven to transition from closed to open. The full syntax for an event handler looks like this:

on <event-id> [(<guard>)] [<action>] [-> <target>];

The things in angle brackets can be arbitrary identifiers that conform to the C language concept of an identifier. Things in square brackets are optional. In the case above the handler includes an optional transition target, but not a guard or action.

Guards and actions can be used to create complex behavior. If a state includes a guarded handler then the user defined function that implements the guard must return a true value for the handler to be triggered. For example:

on foo (some_guard) guarded_action;
on foo default_action;

If a state has the previous two handlers defined and is processing the event foo first the user defined (C language) function some_guard will be called. If its return value is true then the function guarded_action will be called. If some_guard returned 0 then the machine will continue checking for handlers for event foo. The next defined handler is not guarded, so the function default_action will be called.

All actions and guards are implemented by the user as C language functions with the following prototype:

int <function-name>(struct <machine-name> *, struct <machine_name>_event *);

Hierarchical States

To avoid duplicating event handlers for similar states Makina allows you to define sub states that defer unhandled events to their parent states. The closed state of the oven machine might have a few sub states:

machine Oven;
initial state closed {
    on open -> open;
    initial state idle {
        on start -> cooking;
    }
    state cooking {
        entry enable_heater;
        on timeout -> idle;
        exit disable_heater;
    }
}
state open {
    on close -> closed;
    on start error;
}

Now state closed has two sub states: idle and cooking. Additionally the states closed and closed.idle have been designated as initial. This isn't strictly necessary in this case, because default initial states are those appearing first in document order, but has been added to show the syntax. Initial states are the states that are first entered when the machine is initialized.

Since neither sub state of closed defines a handler for the open event if the Oven machine is in either of those states when an open event is processed the parent state's handler, and any associated actions or transitions, will be triggered. In this case the open event will cause a transition to the open state regardless of which sub state was active.
Entry and Exit Actions

Entry and exit actions are similar to event handlers except they are triggered when a state is entered or exited. For example: the entry handler entry enable_heater; in state closed.cooking causes the function enable_heater to be called when that state is entered. Similarly, exit disable_heater; causes disable_heater to be called when state closed.cooking is exited. Exit handlers will be triggered event if the event that causes the transition is defined in a parent state as is the case with the open event in the example above.
Invoking Makina
Get the jar

Clone the repo and build the makina-compiler project using Intellij. Or download the latest jar from here.
Run the compiler

java -jar <path>/<to>/makina-compiler.jar <input-file> [<input-file-2>]

Output

Two files, <machine-name>.h and <machine-name>.c will be created (or overwritten!) in the same directory as <input-file>.