// https://rosettacode.org/wiki/Reverse_a_string
import ballerina/io;
function reverse(string a) returns string {
    string out = "";
    foreach string i in a {
        out = string:concat(i, out);
    }
    return out;
}

public function main() {
    string a = "asdf";
    a = reverse(a);
    io:println(a);
}