Predicate Expressions

Comparison

Several built-in, infix operators allow testing for equality and inequality, including <, >, <=, >=, ==, and !=.

The following are all valid predicate expressions:

c == 5
page:var("city") eq "Blackfoot"
"Lindon" neq location:city()
weather:curr_temp() < 90
location:city() + ", WA" eq city
5 * (weather:curr_temp() - 32) / 9 < 0

As can be seen from the preceding examples, a number of built-in libraries provide predicates that can be used inside predicate expressions. The documentation for those libraries gives details about their operation.

Two special comparison operators are useful with the sort() operator: <=> and cmp. These operators return -1 if the first operand is less than the second, 0, if they're equal, and 1 if the first operand is greater than the second.The <=> operator is used with numbers and cmp is used with strings.

x = 5; 
y = 6;
x <=> y // returns -1
x <=> x // returns 0
y <=> x // returns 1
p = "aab";
q = "abb";
a cmp b // returns -1
a cmp a // returns 0
b cmp a // returns 1

Like

Like takes a regular expression as its second argument and returns true if it matches the string given as its first argument. Arguments to these operators can be any valid expression.

spicy = cheese like re#(nacho|pepperjack)#;

Membership

There is an infix operator for testing membership, ><. The >< operator tests the number or string in the right operand for membership in the map or array given by the left operand. For maps, membership extends to keys only. 

a = [5, 6, 7];
m = {"a" : 1, "b" : 2};
a >< 6     // returns true
a >< 3     // returns false
m >< "a"   // returns true
m >< "foo" // returns false

Compound Predicates

Compound predicate expressions are created using the operators &&, ||, and not to express conjunction, disjunction, and negation, respectively. Conjunction has precedence over disjunction. Parentheses are used to group expressions for precedence.

not a
a && b
a || b
(a || b ) && not c