In Clojure, passing number with leading 0s to str causes strange behavior. What feature is this?

Question

So, I accidentally figured this out while playing around with some strings.

(str 111) => "111"
(str 0111) => "73"

What is this?

Answer 1

Numbers prefixed with 0 are octal:

0111
=> 73

Numbers prefixed with 0x are hexadecimal:

0x111
=> 273

Numbers prefixed with Xr, where X is number from 2 to 36, have that radix:

2r111
=> 7

If you want to pad number with zeros, see format or cl-format:

(format "%04d" 111)
=> "0111"

(clojure.pprint/cl-format nil "~4,'0d" 111)
=> "0111"