--- a/scripts/control/system/sysdisc.m
+++ b/scripts/control/system/sysdisc.m
@@ -36,63 +36,66 @@
 
 function [dsys, Adc, Cdc] = sysdisc (sys)
 
-  save_empty = empty_list_elements_ok;
-  empty_list_elements_ok = 1;
+  save_warn_empty_list_elements = warn_empty_list_elements;
+  unwind_protect
+    warn_empty_list_elements = 0;
 
-  if (nargin != 1)
-    usage("[dsys,Adc,Cdc] = sysdisc(sys)");
-  elseif (!isstruct(sys))
-    error("sys must be in system data structure form");
-  endif
+    if (nargin != 1)
+      usage("[dsys,Adc,Cdc] = sysdisc(sys)");
+    elseif (!isstruct(sys))
+      error("sys must be in system data structure form");
+    endif
 
-  sys = sysupdate (sys, "ss");
-  [n_tot, st_c, st_d, y_c, y_d] = __syscont_disc__ (sys);        # get ranges
+    sys = sysupdate (sys, "ss");
+    [n_tot, st_c, st_d, y_c, y_d] = __syscont_disc__ (sys);        # get ranges
 
-  ## assume there's nothing there; build partitions as appropriate
-  Add = Adc = Bdd = Cdd = Cdc = Ddd = [];
+    ## assume there's nothing there; build partitions as appropriate
+    Add = Adc = Bdd = Cdd = Cdc = Ddd = [];
 
-  if(isempty(st_d) & isempty(y_d))
-    error("sysdisc: expecting discrete states and/or continous outputs");
-  elseif (isempty(st_d))
-    warning("sysdisc: no discrete states");
-  elseif(isempty(y_d))
-    warning("sysdisc: no discrete outputs");
-  endif
+    if(isempty(st_d) & isempty(y_d))
+      error("sysdisc: expecting discrete states and/or continous outputs");
+    elseif (isempty(st_d))
+      warning("sysdisc: no discrete states");
+    elseif(isempty(y_d))
+      warning("sysdisc: no discrete outputs");
+    endif
 
-  [aa,bb,cc,dd] = sys2ss(sys);
-  if(!isempty(st_d) )
-    Add = aa( st_d , st_d);
-    stname = sysgetsignals(sys,"st",st_d);
-    Bdd = bb( st_d , :);
-    if(!isempty(st_c))
-      Adc = aa( st_d , st_c);
+    [aa,bb,cc,dd] = sys2ss(sys);
+    if(!isempty(st_d) )
+      Add = aa( st_d , st_d);
+      stname = sysgetsignals(sys,"st",st_d);
+      Bdd = bb( st_d , :);
+      if(!isempty(st_c))
+	Adc = aa( st_d , st_c);
+      endif
+      if(!isempty(y_d))
+	Cdd = cc(y_d , st_d);
+      endif
+    else
+      stname = [];
     endif
     if(!isempty(y_d))
-      Cdd = cc(y_d , st_d);
-    endif
-  else
-    stname = [];
-  endif
-  if(!isempty(y_d))
-    Ddd = dd(y_d , :);
-    outname = sysgetsignals(sys,"out",y_d);
-    if(!isempty(st_c))
-      Cdc = cc(y_d , st_c);
+      Ddd = dd(y_d , :);
+      outname = sysgetsignals(sys,"out",y_d);
+      if(!isempty(st_c))
+	Cdc = cc(y_d , st_c);
+      endif
+    else
+      outname=[];
     endif
-  else
-    outname=[];
-  endif
-  inname = sysgetsignals(sys,"in");
-  outlist = 1:rows(outname);
+    inname = sysgetsignals(sys,"in");
+    outlist = 1:rows(outname);
 
-  if(!isempty(outname))
-    tsam = sysgettsam(sys);
-    [nc,nz] = sysdimensions(sys);
-    dsys = ss2sys(Add,Bdd,Cdd,Ddd,tsam,0,nz,stname,inname,outname,outlist);
-  else
-    dsys=[];
-  endif
+    if(!isempty(outname))
+      tsam = sysgettsam(sys);
+      [nc,nz] = sysdimensions(sys);
+      dsys = ss2sys(Add,Bdd,Cdd,Ddd,tsam,0,nz,stname,inname,outname,outlist);
+    else
+      dsys=[];
+    endif
 
-  empty_list_elements_ok = save_empty;
+  unwind_protect_cleanup
+    warn_empty_list_elements = save_warn_empty_list_elements;
+  end_unwind_protect
 
 endfunction