#*
 A demonstration of parsing palindromes with the 
 parse machine language. This looks much less elegant
 than one would expect. A recursive palindrome recogniser
 in c or forth is much more elegant.

 Also, this doesnt really work because "aaabbbaaa" is
 rejected as a palindrome. This is because it contains sub
 palindromes "aa", "aaa", "bb", "bbb" etc
 Added "pal*pal*pal*" and "pal*c*pal*" to a block test.
 Had the idea to read all letter blocks (eg: "aaa" "bbb") in
 one go instead of letter by letter.
*#

 read; 
 [:space:] { clear; .reparse }
 put; clear; add "c*"; push; 

parse>

 pop; pop;
 "c*c*" { 
    swap; ++; 
    (==) { 
      --; swap; 
      clear; 
      get; ++; get; --; put; clear;
      add "pal*"; push;
      .reparse  # also, catch EOF condition
    } 
    --; swap;
 } 
 push; push;

 pop; pop; pop;

 "pal*c*pal*",  
 "pal*pal*pal*",  
 "c*pal*c*",  
 "c*c*c*" { 
   swap; ++; ++;
   (==) {
     --; --; swap;
     clear;
     get; ++; get; ++; get; --; --; put; 
     clear;
     # print found palindromes
     add "found palindrome: "; get; add "\n";  
     print; clear;
     add "pal*"; push;
     .reparse
   }
   --; --; swap;
 }

 push; push; push;
 
 (eof) {
   pop; 
   "pal*" { 
     clear; 
     add "characters read: "; cc; add "\n";
     add "its a palindrome! ("; get; add ")\n";
     print; 
     clear; quit;
   }
   state;
   clear; add "nope not a palindrome... \n"; print; quit;
 }