module main

// note missing `input` argument in fn signature
fn foo() !string {
	// without next error does not occurs
	a, b := input.split_once('%') or { '', 'empty' }
	if b == '' {
		return error('')
	}
	return a
}

fn main() {
	res := foo('fe80::1234%ne0') or {
		eprintln(err)
		exit(1)
	}
	println(res)
}