Error handling

import ballerina/io;

// Converts `bytes` to a `string` value and then to an `int` value.
function intFromBytes(byte[] bytes) returns int|error {

    string|error ret = string:fromBytes(bytes);

    // The `is` operator can be used to distinguish errors from other values.
    if ret is error {
        return ret;
    } else {
        return int:fromString(ret);
    }
}

// The `main` function can return an `error` value.
public function main() returns error? {

    int|error res = intFromBytes([104, 101, 108, 108, 111]);
    
    if res is error {
        // The `check` expression is the shorthand for this pattern of
        // checking if a value is an `error` value and it is returning that value.
        return res;
    } else {
        io:println("result: ", res);
        return;
    }
}