2015-06-22: add newbase60 example with integer->sxg

add newbase60 example with integer->sxg

diff --git a/examples/newbase60.w b/examples/newbase60.w
--- a/examples/newbase60.w
+++ b/examples/newbase60.w
@@ -2,8 +2,39 @@
 exec guile -L $(dirname $(dirname $(realpath "$0"))) --language=wisp -e '(@@ (examples newbase60) main)' -s "$0" "$@"
 ; !#
 
+;; Encoding and decoding numbers in New Base 60 as defined by Tantek:
+;; http://tantek.pbworks.com/NewBase60
+
+;; Based on the very elegant implementation from kevin marks:
+;; https://github.com/indieweb/newBase60py/blob/master/newbase60.py
+
 define-module : examples newbase60
               . #:export : main
+              . #:use-module : srfi srfi-1
+
+define base60letters "0123456789ABCDEFGHJKLMNPQRSTUVWXYZ_abcdefghijkmnopqrstuvwxyz"
+define base60numbers
+       append
+         map cons (string->list base60letters) : iota : string-length base60letters
+         quote
+           : 
+             #\l . 1 ; typo lowercase l to 1
+             #\I . 1 ; typo capital I to 1
+             #\O . 0 ; typo capital O to 0
+
+define : integer->sxg num
+         if : equal? 0 num
+            . "0"
+            let loop
+               : s '()
+                 n num
+               if : equal? n 0
+                    list->string : reverse s
+                    loop
+                      cons 
+                        string-ref base60letters (remainder n 60)
+                        . s
+                      quotient n 60
 
 define : main args
-         display args
+       display : integer->sxg 61