The missing function can be used to check the status of the function arguments. It returns a boolean vector which has one element for each argument. If an element of the vector has the value T, it indicates that the corresponding argument was missing and was filled in by a default value as a result. The following two functions,
func m1(...=0) missing()
func m2(a=1,b=2,c=3,...) missing()
simply return the result of the call to missing. The result of the
following invocation,
m1(2,3,,5,)is [F, F, T, F, T]. This indicates that the third and fifth parameters were missing. The results of the following two invocations,
m2(2,,3,4,5)
m2(2)
are [F, T, F, F, F] and [F, T, T] respectively. The first
result indicates that only the second parameter was missing, while the
second indicates that the second and third parameters were missing.