Comparison
Several built-in, infix operators allow testing for equality and inequality, including <
, >
, <=
, >=
, ==
, and !=.
The following are all valid predicate expressions:
c >= 5 event:attr("city") != "Blackfoot" "Lindon" == app:cities[random:integer(0, app:cities.length()-1)] time:now() == time:new("2015-08-08") 5 * (random:number(32, 212) - 32) / 9 < ent:thresholdTemp
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