Represents a node during the slicing process, together with the environment it is traversed in
(modified by function calls) and whether it is only used for its side effects.
if we add a function call, we may need it only for its side effects (e.g., a redefinition of a global variable), if so, 'returns' links will not be traced
Represents a node during the slicing process, together with the environment it is traversed in (modified by function calls) and whether it is only used for its side effects.