/*** Syntax ***/
void function_name(a, {opt_param1, opt_param2}) { }

/*** Example ***/
print_fruits(a,{b,c}) {
   print("a: " + a.toString() +
         " , b: "+ b.toString() +
         " , c: " + c.toString());
}

print_fruits('apple');
print_fruits('apple',b:'guava');
print_fruits('apple',c:'guava',b:'mango');

/** Output
  a: apple , b: null , c: null
  a: apple , b: guava , c: null
  a: apple , b: mango , c: guava
*/