Decorator

Action!(Leaf!Ternary, process) a;
Decorator!(Action!(Leaf!Ternary, process), Not) d1; 

Functor v; 
v = 0; 
auto res = a(v, 10); 
assert(v == 10); 
assert(res == Ternary.no); 
v = 0; 
res = d1(v, 10); 
assert(v == 10); 
assert(res == Ternary.yes); 

v = 50; 
res = a(v); 
assert(v == 500); 
assert(res == Ternary.unknown); 
v = 50; 
res = d1(v); 
assert(v == 500); 
assert(res == Ternary.unknown); 

v = 5; 
res = a(v, 10, 10, 10, 10, 10); 
assert(v == 55); 
assert(res == Ternary.yes); 
v = 5; 
res = d1(v, 10, 10, 10, 10, 10); 
assert(v == 55); 
assert(res == Ternary.no); 

Condition!(Leaf!bool) c;
Decorator!(Condition!(Leaf!bool), Not) d2; 
v = 0; 
res = c(v, 10); 
assert(v == 10); 
assert(res == Ternary.no); 
v = 0; 
res = d2(v, 10); 
assert(v == 10); 
assert(res == Ternary.yes); 

v = 5; 
res = c(v, 10, 10, 10, 10, 10); 
assert(v == 55); 
assert(res == Ternary.yes); 
v = 5; 
res = d2(v, 10, 10, 10, 10, 10); 
assert(v == 55); 
assert(res == Ternary.no);