/**
* Return the Element which corresponds to the given variable name. It will first check local
* variables and then the parent context. This method will return null if the variable doesn't
* exist or the argument is null. Note that this will clone the final value, if it originated from
* a global variable.
*
* @param name name of the variable to lookup
* @param lookupOnly flag indicating if only a lookup should be done
* @param terms values for dereferencing the given variable
* @return Element value of the associated dereferenced variable
*/
public Element dereferenceVariable(String name, boolean lookupOnly, Term[] terms)
throws InvalidTermException {
boolean duplicate = false;
Element result = localVariables.get(name);
// If the result is null, then try to look up a global variable.
if (result == null) {
duplicate = true;
result = getGlobalVariable(name);
}
// Now actually dereference the given variable. The caller must deal
// with any invalid term exceptions or evaluation exceptions. We just
// pass those on.
if (result != null) {
if (!(result instanceof Undef)) {
// FIXME: Determine if the result needs to be protected.
result = result.rget(terms, 0, false, lookupOnly);
} else {
// Trying to dereference an undefined value. Therefore, the
// value does not exist; return null to caller.
result = null;
}
}
// FIXME: This is inefficient and should be avoided. However, one must
// ensure that global variables are protected against changes.
// To ensure that global variables are not inadvertently modified via
// copies in local variables, duplicate the result. Do this only AFTER
// the dereference to limit the amount of potentially unnecessary
// cloning.
if (duplicate && result != null) {
result = result.duplicate();
}
return result;
}
