Default action (give just a warning?) of non-defined variables

[Heikki Johannes Junes]

Would there be any sence if the default action of a non-defined variable
would be `give just a warning'? I would like to do the following

% mysong.ly
% \global is not defined
myMusic = { c4 d }
myWordsA = { Hel- lo }
myWordsB = { fel- low }
% \myWordsC, \myWordsD, and \myWordsE are not defined
\include "songtemplate.ily"

% songtemplate.ily
\score {
   \new Staff <<
      \context Voice = myvoice { \voiceOne << \global \myMusic >> }

      \context Lyrics = myvoiceA { s1 }
      \context Lyrics = myvoiceB { s1 }
      \context Lyrics = myvoiceC { s1 }
      \context Lyrics = myvoiceD { s1 }
      \context Lyrics = myvoiceE { s1 }
      \context Lyrics = myvoiceA \lyricsto myvoice \WordsA
      \context Lyrics = myvoiceB \lyricsto myvoice \WordsB
      \context Lyrics = myvoiceC \lyricsto myvoice \WordsC
      \context Lyrics = myvoiceD \lyricsto myvoice \WordsD
      \context Lyrics = myvoiceE \lyricsto myvoice \WordsE
   >>
}

-- 
Terveisin
Heikki Junes