[FEATURE] Rust-like or Java-like Error handling from function return

[vladceresna]

Now, as I understood from documentation on wren.io, we don't know what we will get from the function - which type, class, object, or just our program will be shutting down because we have error in some place in function.

So, we need to have normal error handling features. And I have 2 thoughts about how we can implement it in Wren.

1. Rust-like - Results with Errors and unwrap()

ourFunction(input) -> Result<String, Error> {
    return Ok("") // or return Err("Message")
}
System.print(ourFunction("").unwrap())
match ourFunction("") {
    Ok(v) -> System.print(v),
    Err(e) -> System.print(e)
}

This way needs Enums to be implemented already.

2. Java-like - Exceptions and try/catch

ourFunction(input) throws Exception -> String {
    return "" // or throw Exception("")
}
try {
    ourFunction("")
} catch(e) {
    System.print(e)
}

So, I prefer Rust-like style, but I think, we need more thoughts from other developers for understand, what actually is really to implement in small Wren nature and which syntax is better to use in this cases.

Also, I think, good point is to have ability to mention type of value, which we return from function or get in function. Because it will rank up safety and, perspectively, performance of code, written in Wren.

Thanks for your work!

[vladceresna]

Now I have an idea how this can be done as Rust-style even without generics, simply by having a convention in the project regarding what will always be returned in functions. And there is no need to change the Wren core here either. We can simply create a Return class and return it from functions. We can also perform actions depending on the status of the result (success or failure). The dynamic nature of Wren has a positive impact on the possibility of implementing this.

import "virtel/ui" for UI
import "virtel" for Center, VirtelApp, Log

class CalculatorApp is VirtelApp {
    static start() {
        UI.createWindow("Calculator", 500, 500)
        Log.success("Window shown.")
        Log.info(add(5,6).unwrap().toString)
    }
    static add(a,b) {
    		return Result.ok(a+b) // return Result.error("Message")
    }
    
}

class Result {
	construct ok(data) {
		_data = data
		_status = true
	}
	construct error(msg) {
		_msg = msg
		_status = false
	}
	status { _status }
	msg { _msg }
	data { _data }
	unwrap() {
		if (_status) {
			return _data
		} else {
			Log.error(_msg)
		}
	}
}

And this code is already tested on my Virtel project, which is box for running Wren apps by running VirtelApp.start().

[vladceresna]

Now I understand that most errors can come from the Wren API library itself, so it would be good to either make them all return Result, or make it possible to intercept them with a try/catch block.

[vladceresna]

Now we only have this method of error handling, as I understand from the documentation, but in my opinion, it's too much to run a separate coroutine to handle the error in it.

var safeExec = Fn.new {
  var list = [1, 2, 3]
  list[100]
}

var errorMsg = Fiber.try(safeExec)

if (errorMsg) {
  System.print("Message: %(errorMsg)")
} else {
  System.print("Without error")
}