if ~ defined label
; ... code
end if    

macro label arg
{
local d, l, m
; Check if already defined
   match =arg, arg\{d equ\}
   match d,d\{err 'Already defined'\}

   match name opts, arg
   \{
      label l opts
      name equ l
      m equ
   \}
   match m, m
   \{
      label l
      arg equ l
   \}
}
macro undefine name
{
   match =name, name\{err 'No such label'\}

   restore name
}

label foo byte

if ~defined foo
  display "1. Not defined"
end if

undefine foo

if ~defined foo
  display "2. Not defined"
end if    

macro label [args]
{
  common local name
   match \name opts,args \{ name equ \name \}
    match =name,name \{ name equ args \}
    match \name,name
   \{
            if ~defined \name\#.undefined
                     label args
          end if
      \}
} 
macro undefine name
{
        local undef
 if defined name#.undefined & ~defined undef
             display 'The label "',`name,'" is already undefined',13,10
            err
 end if
      name#.undefined = 1
 undef = 1
}

undefine foo

label foo byte

if defined foo
 display 'Defined',13,10
else
   display 'Not defined',13,10
end if    

struc GlobalStruc
{ 
.code:
 };define actual code.

.localName GlobalStruc;define Single-Use struc.