PTOLEMY II - CiteSeerX

that match. Thus, for example,
{foodCost=40, hotelCost=100} + {foodCost=20, taxiCost=20}
yields the result
{foodCost=60}
Expressions
You can think of an operation as a set intersection, where the operation specifies how to merge the values
of the intersecting fields. You can also form an intersection without applying an operation. In this
case, using the intersect() function, you form a record that has only the common fields of two specified
records, with the values taken from the first record. For example,
>> intersect({a=1, c=2}, {a=3, b=4})
{a=1}
Records can be joined (think of a set union) without any operation being applied by using the
merge() function. This function takes two arguments, both of which are record tokens. If the two
record tokens have common fields, then the field value from the first record is used. For example,
merge({a=1, b=2}, {a=3, c=3})
yields the result {a=1, b=2, c=3}.
Records can be compared, as in the following examples:
>> {a=1, b=2}!={a=1, b=2}
false
>> {a=1, b=2}!={a=1, c=2}
true
Note that two records are equal only if they have the same field labels and the values match. As with
scalars, the values match irrespective of type. For example:
>> {a=1, b=2}=={a=1.0, b=2.0+0.0i}
true
The order of the fields is irrelevant. Hence
>> {a=1, b=2}=={b=2, a=1}
true
Moreover, record fields are reported in alphabetical order, irrespective of the order in which they are
106 Ptolemy II