dirigent

ChatGPT-generated readme

The term "dirigent" is derived from the Latin word "dirigere," which means "to guide" or "to direct". In music, a "dirigent" is another term for a conductor, the individual who guides and directs an orchestra or choir during a performance. They ensure that all parts of the ensemble play together in harmony, keeping to the correct tempo and dynamics, and making sure each section comes in or stops at the right times.

This tool is a system that orchestrates the execution of a series of steps or operations, ensuring they are performed in the correct sequence. Just like a musical conductor, it manages the flow and progression of state through a series of transformations (steps), and makes sure each step receives the correct input (the current state) and passes its output (the new state) to the next step in sequence.

stateDiagram-v2
    state "lib/json-equal" as s0
    state "core" as s1
    state "util" as s2
    state "persistence/fs" as s3

    s1 --> s2
    s1 --> s0
    s3 --> s1

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The provided code is written in TypeScript. This code defines a series of constructs related to the concept of a 'Step', which is an operation that transforms a state S in some way.

Here's a detailed breakdown:

1. interface Step<S>: This interface represents an abstraction of a 'step'. Any class implementing this interface must provide an execute function that takes a state S and returns a possibly modified state S. The returned state can be either a simple value or a Promise that resolves to a value.

2. class StepSequence<S> implements Step<S>: This class implements the Step interface for a sequence of steps. It takes an array of steps in its constructor and executes them in sequence when its execute function is called.

3. stepLoop<S>(steps: Step<S>[], state: S): Promise<S>: This is an asynchronous helper function used by StepSequence to execute a sequence of steps. It iterates over each step, freezes the state to prevent unwanted mutations, and then executes the step. The result of each step is fed as the state into the next one. The final state is returned as a promise.

4. deepFreeze(obj: any): typeof obj: This function recursively freezes an object and all its properties using Object.freeze, which prevents them from being modified. This is used in stepLoop to prevent steps from modifying the state directly.

5. deepClone<S>(s: S): S: This function makes a deep copy of an object by converting it to a JSON string and then parsing it back to an object. This creates a new copy of the object that shares no references with the original.

The overall purpose of this code is to execute a sequence of 'steps' in a controlled and safe manner. Each step gets a frozen copy of the current state, which it can use to produce a new state without affecting the old one. This could be used, for example, in a state machine or game engine where each step represents a game tick, player action, or AI decision.

Example 1

To run example:

vr example-01

Sample code:

const initialState: State = {
  history: [],
};

const steps = new StepSequence<State>([
  new AppendStep(1),
  new StepSequence<State>([
    new AppendStep(2),
    new AppendStep(3),
    new AppendStep(4),
  ]),
  new AppendStep(5),
]);

const newState = await steps.execute(initialState);

assertEquals(newState.history, [1, 2, 3, 4, 5]);

Firstly, a new type State is defined. This state is an object that holds a single property: history which is an array of numbers.

Next, a new class AppendStep implementing the Step interface is defined. AppendStep essentially represents a step in the process that appends a number to the history array. It does this in a non-mutative way, by creating a deep clone of the current state, modifying this clone, and then returning it.

Finally, a test case is defined to check whether the step-based logic works as expected. In the test, an initial state is defined with an empty history array. A sequence of steps is then created. This sequence includes a mix of individual AppendStep instances and nested StepSequence instances, mimicking a complex scenario.

The stepLoop function is called with this array of steps and the initial state. The stepLoop function executes each step in order, each time passing the newly returned state into the next step. The result is a final state that has passed through all the steps.

The test then verifies that the history property of the final state matches the expected sequence of numbers, [1, 2, 3, 4, 5]. If the history array is as expected, it means that all the steps have been executed correctly in the correct order.

Example 2 (plain file persistence)

vr example-02

cat /tmp/state.json | jq '.'

{
  "history": [
    1,
    2,
    3,
    4,
    5
  ]
}