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Comment by Byamarro | Hacker News Reader

Incredible, it's like having perfectly typed language without having to use types at all. Few worries from my side:

- TypeScript gained traction partially because you could migrate an existing codebase to it. Does leporello support gradual migration from style that's not aligned with leporello to the supported subset? That is, how leporello handles a codebase that's partially written in freestyle JS and not the subset that leporello specify handles?

- How does it deal with patterns from popular frameworks or libraries that are borderline frameworks. React, Vue, Express, NestJS etc.

- It feels like leporello has to store a lot of possible branch-outs of the state. How would it handle frameworks code in this case? React on its own probably has a lot of branch-outs inside. Would it devour my RAM?

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>> How does it deal with patterns from popular frameworks or libraries that are borderline frameworks. React, Vue, Express, NestJS etc.

React is a great fit for Leporello.js. There is an example of React TODO app that you can write and debug in Leporello. It is showcased in the video. You can play with it yourself if follow the link https://app.leporello.tech/?example=todos-preact

Speaking about backend frameworks, basically you code is a function Request -> Response. How do you organize your code is up to you. You can code it in a functional manner. What is great about Leporello, is that it remembers all the calls your app made to databases, other microservices and external APIs and allows to debug them in a time-travel manner, seeing requests and responses. You can run your code once, and then debug and navigate it forward and backward, seeing runtime values that were generated when your code was executed. It a huge time saving, especially when external resources are slow and may require complex setup or teardown before or after being called.

>> It feels like leporello has to store a lot of possible branch-outs of the state

Could you please clarify, what do you mean by branch-outs of the state?

>> That is, how leporello handles a codebase that's partially written in freestyle JS and not the subset that leporello specify handles?

Leporello is based on the idea that you can have much more powerful dev experience (time-travel debugging, better debugger UX) if you adhere to functional code. Look at the recent news from Jetbrains [0]. They presented predictive debugger for their .NET IDE. They called it "a game changing look into the future" and it is actually a huge improvement of ergonomics. But with FP, you get predictive debugger for free. It is just a trivial consequence of not having data mutations. So inside the function, each name is binded to single immutable value.

If you have freestyle JS, then Leporello is not a good fit for you. It requires some buy-in from a developer. The good thing is that you still write plain vanilla javascript, without non-standart extensions that require some kind of transpilation.

[0] https://news.ycombinator.com/item?id=36940937

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