Sets the value of an attribute on a record
// Set attribute to value record.attribute := value // Remove attribute record.attribute := none
record.attribute := value sets
record already has an attribute with a value, then this will overwrite it. Otherwise, if
record doesn’t have an attribute with this name already, then
:= will create the attribute and set it to
attribute can be an attribute already on the record, or it can be a new attribute.
value can be a string or number literal, a record, or a variable bound to one of these.
record.attribute := none sets the value of
attribute to the special value
none, which is the empty set (a set with no elements).
#students that don’t already have an age.
search student = [#student] age = if student.age then student.age else if student.grade then student.grade + 6 bind student.age := age