Module Checkit {
      \\
      \\ Part 1: Make global variable, alter it, make a shadow local or global one, use temporary variable
      \\
      Global a$="ok"
      Module Global What {
            Print a$
      }
      Module Checkit {
            Print a$="ok"
            a$<=""
            Print a$=""
            a$<="ok2"
            a$=""
            Print a$="", a$<>""
            Global  a$="ok again"
            Module Inner {
                  Print a$="ok again"
            }
            Inner
            What   \\ now What use new global a$
            \\ display list of public variables
            List
            \\ we can define locals using Def, but raise error if local exist
            Try {
                  Def a$="error"
            }
            Def b$
            Print b$=""
            For This {
                  \\ block for temporary definitions
                  For i=1 to 10 {
                        Local a$=str$(i)
                  }
                  \\ we get 10 more a$
                  List
                  Print a$=" 10"
            }
            Print a$=""
            List
            \\ using current stack
      }
      \\ we call always a local module, or a global, but not this module,
      \\ no recursion for standard call for modules.
      \\ we have to use Call Checkit to call this module recursive
      Checkit
      What  \\ now what use old global a$
      Print a$<>""  ' true
      List

      \\
      \\ Part 2:  Pass an empty string to a variable through stack of values
      \\
      Module Checkit2 {
             \\ read make a local by default
             Read a$
             Print a$=""  ' true
             For This {
                   Push "Hello"
                   Read New a$
                   Print a$="Hello"
                   List
            }
            Print a$=""
      }
      Checkit2 ""
      Print a$<>""  ' true
      Module Checkit3 {
            \\ using Set we change to global  space, for the end of line
             Set Read a$
             Print a$=""  ' true
             list
      }
      Checkit3 ""
      Print a$<>"" ' true
      Module Checkit4 {
            \\ this make a local if no global exist
            \\ so if global exist, alter the global one
             Let a$=Letter$
             Print a$=""  ' true
             list
      }
      Checkit4 ""
      Print a$="" ' true
}
Checkit