[Jprogramming] Value error with ;

[Anssi Seppälä]

Keeping data in structure with ; is a great thing. However I do not understand the logic to get value error:

   value=: 123

   novalue
|value error: novalue

   (1 2 3);'abc';value;novalue
1 2 3 ; 'abc' ; 123 ; novalue	NB. No value error with novalue

   (1 2 3);'abc';novalue;value 
|value error: novalue		NB. Now J gives value error with novalue
|   (1 2 3);'abc';    novalue;value

Is there any method to always observe that novalue is not defined?

Regards,
Anssi