управление односвязным списком(частично решено)

program lists;
uses crt;
type
Tlist=^Trec;
Trec=record
data:integer;
next:tlist;
end;
var
list,lend:tlist;
wht:char;
x:integer;
flag:boolean;
 
function addtolistbegin(var l:Tlist; newdata:integer): boolean;
var newEL:tlist;
Begin
new(NewEL);
newel^.data:=newdata;
newel^.next:=l;
l:=newel;
addtolistbegin:=true;
end;
 
 
 
procedure display(l:tlist);
begin
if l=nil then writeln('list is empty')
else while l<>nil do begin
write(l^.data:4);
l:=l^.next
end;
writeln;
end;
 
procedure delfrbeg(var l:tlist;x:integer);
var newel:tlist;
begin
if L=nil then
writeln('list is empty')
else
begin
newel:=l;
l:=l^.next;
x:=newel^.data;
dispose(newel);
end;
end;
 
 
Begin
list:=nil;
clrscr;
flag:=true;
while flag do begin
writeln('0 - exit');
writeln('1 - add to begin');
writeln('2 - add to end');
writeln('3 - delete from begin');
writeln('4 - delete ftom end');
writeln('5 - delete all');
writeln('6 - display');
readln(wht);
case wht of
'0': flag:=false;
'1': begin
writeln('vvedite znachenie');
readln(x);
addtolistbegin(list,x);
end;
'2': begin
writeln('vvedite znachenie');
readln(x);
addtolistend(list,x);
end;
'3':
delfrbeg(list,x);
'4':
delfrend(list,x);
{'5': deleteall(list);}
'6': display(list);
end;
end;
end.