/* 

  Shortest code to encrypt string in Picat.

  http://codegolf.stackexchange.com/questions/20021/shortest-code-to-encrypt-a-string
  """
  Using a language of your choice write a program that takes a string as an input, 
  and returns the string encrypted.

  Algorithm:
  
  You should assume that each character is always encoded in a byte and is ASCII-based. 
  The extended ASCII codes are mapped to whatever is the default code page in use 
  by the system.
  
  You should encrypt the code in the following way: code of first character +1, code of second 
  character +2, code of third character +3 .....
  
  Extended ASCII codes are based on this table: http://www.asciitable.com/
  
  Shortest code wins.  
  """
  

  This program was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/

main => go.

go ?=>
  S = "My secret password is 123456!",
  E = encrypt1(S),
  println(encrypt1=E),
  println(decrypt1=decrypt1(E)),
  
  nl.
go => true.


% 42 chars
encrypt1(S) =
%          1         2         3         4     42 chars
% 123456789012345678901234567890123456789012
  [chr(ord(C)+I):{C,I}in zip(S,1..S.length)].
%   I:=0,[chr(ord(C)+I):C in S,I:=I+1]=E. % Error: assignment_in_condition::=/2 ["works" in Picat shell]

% decrypt: 42 chars
decrypt1(S) =
  [chr(ord(C)-I):{C,I}in zip(S,1..S.length)].