\ Copyright (C) 2015 by Alexandru Cojocaru

\ This program is free software: you can redistribute it and/or modify
\ it under the terms of the GNU General Public License as published by
\ the Free Software Foundation, either version 3 of the License, or
\ (at your option) any later version.

\ This program is distributed in the hope that it will be useful,
\ but WITHOUT ANY WARRANTY; without even the implied warranty of
\ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
\ GNU General Public License for more details.

\ You should have received a copy of the GNU General Public License
\ along with this program.  If not, see <http://www.gnu.org/licenses/>.

: len 'z' 'a' - 1 +  ;
: inrange? rot tuck >= -rot <= and ;
: rotc tuck - 13 + len mod + ;
: rot-lower dup 'a' 'z' inrange? if 'a' rotc then ;
: rot-upper dup 'A' 'Z' inrange? if 'A' rotc then ;
: rot13 dup 0 u+do over dup i + c@ rot-lower rot-upper swap i + c! loop ;

s" The butler did it!" rot13 type