merkle reverse

[aerto]

This is the bitcoin genesis block merkle root 
4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b 
how i can get it at this format 
3ba3edfd7a7b12b27ac72c3e67768f617fc81bc3888a51323a9fb8aa4b1e5e4a 
??

i try it using

string merkle = 
"4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b";

writeln(merkle.retro.text); and it gives me

b33adedfa7b7212ba77cc2e37667f816f78cb13c88a81523a3f98baab4e1e5a4