interaction
  (new(x:<t>out)):<t>ref
interaction
  (make(x:<t>out)flow):activation in
is
  ((x)=((new(x))default(previous(x))))
with
  interaction
    ((x:<t>in)default(y:<t>in)):<t>out
  is
    ((res) with behavior (
      (apply (f) to ({x:(x),y:(y)}) and send to (res))
    ))
  with
    interaction
      (res):<t> ref
    interaction
      (f):{x:<t>,y:<t>}-><t> out
    is
      (`
      if(in.x.active){
        out = in.x;
      } else {
        out = in.y;
      }
      `)











typedef struct {
  number x;
  number y;
} f_in;

typedef number f_out;

void f(f_in* in, f_out* out){
  if(*(in).x.active) {
    *out = *(in).x;
  } else {
    *out = *(in).y;
  }
}