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A. M. DeWitt wrote on Mon, May 10, 2021 06:57 PM UTC:

I have a quick programming question. For my Taishin Shogi preset, I am developing code to enforce the rules. I have all the piece functions done except for those for the Emperor (promoted King). The relevant code is listed below.

// Royals

def +k not sub EMPEROR #1 and <= distance #0 #1 24;
def +K not sub EMPEROR #1 and <= distance #0 #1 24;

def +kX spaces and #0;
def +KX spaces and #0;

// Subroutines

set broyals cp k +de +cp +k;
set wroyals CP K +DE +CP +K;

sub EMPEROR to; // Emperor
  if match moved (intersection nolower #wpieces):
    if match old #broyals:
      if sub checked #to;
        return true;
      else:
        return false;
      endif;
    else:
      return false;
    endif;
  else:
    if match old #wroyals:
      if sub checked #to;
        return true;
      else:
        return false;
      endif;
    else:
      return false;
    endif;
  endif;
endsub;

// This subroutine checks whether a King is in check.

sub checked king:
  my from piece;
  if match cond empty #king moved space #king (intersection nolower #wpieces):
    def enemies intersection noupper #bpieces;
  else:
    def enemies intersection nolower #wpieces;
  endif;
  for (from piece) fn enemies:
    if fn #piece #from #king:
      return #from;
    endif;
  next;
  return false;
endsub;

// Stalemated Subroutine

sub stalemated kingpos:
  store;
  local from piece to;

  if isupper #kingpos:
    def friends intersection nolower #wpieces;
    def friend match #0 #wpieces;
  else:
    def friends intersection noupper #bpieces;
    def friend match #0 #bpieces;
  endif;

  set firstpart true;
  store;
  
 // Can any piece legally move?
  for (from piece) fn friends:
    for to fn join #piece X #from:
      if fn #piece #from #to and not fn friend space #to and onboard #to:
        move #from #to;
            setlegal #from #to;
      endif;
      restore;
    next;
  next;

  // All done. Set $legalmoves and return;
  return cond count system legalmoves false true;
endsub;

The EMPEROR subroutine is written so that moves that capture protected enemy royals with an EMPEROR are treated as illegal, but it does not affect the display of legal moves. My question is how to rewrite it so that if an enemy royal is protected, a legal move will not be displayed (the corresponding stalemated subroutine is provided for convenience). Any help would be much appreciated.