Composition (JOIN)

The composition operator creates a property whose value is another property — the main property — applied to the values returned by other properties supplied as its arguments.

The result class is the value class of the main property.

Language

To implement composition, use the JOIN operator.

Examples

f = DATA INTEGER (INTEGER, INTEGER, INTEGER);
g = DATA INTEGER (INTEGER, INTEGER);
h = DATA INTEGER (INTEGER, INTEGER);
c(a, b) = f(g(a, b), h(b, 3), a);

count = DATA BPSTRING[255] (INTEGER);
name = DATA BPSTRING[255] (INTEGER);
formatted(INTEGER a, INTEGER b) = [FORMULA BPSTRING[255] ' CAST($1 AS TEXT) || \' / \' || CAST($2 AS TEXT)'](count(a), name(b));

CLASS Triangle;
cathetus1 = DATA DOUBLE(Triangle);
cathetus2 = DATA DOUBLE(Triangle);

hypotenuseSq(triangle) = cathetus1(triangle)*cathetus1(triangle) + cathetus2(triangle)*cathetus2(triangle);

// a similar property set using composition
hypotenuseSq2(triangle) = [ x*x + y*y](cathetus1(triangle), cathetus2(triangle));