shelf-type argument-name (is | isnt) specified

Used to test if the value of a variable or attribute has been specified. It has two applications: pattern variables and optional arguments of functions.

You can test a pattern variable to see if any value was assigned to it. Note that there is a difference between having no value assigned and having a value of empty string ("") assigned. A pattern variable is only unspecified if it is inside a pattern that is matched zero times. If it is assigned the value of a whole pattern that is matched zero times, it has the value of empty string (""). Thus this program:

  process
     submit "aaaaaazzzzzz"

  find "a"+ ("b" => found-1)? => found-2 "z"+
     output "found-1 is unspecified%n" when found-1 isnt specified
     output "found-2 is empty string%n" when found-2 = ""

  found-1 is unspecified
  found-2 is empty string

If you write a function that has optional arguments, you should test to make sure that the optional argument was specified in the function call before you attempt to use the argument:

  define function foo (
     value stream first,
     value stream second optional) as

     output first
     output second when second is specified

  process
     foo("one%n")
     foo("two%n", "three%n")

If you supplied a default value for the argument, you can use it safely even if it is not specified. The is specified test will still return false for an unspecified argument even if you give it a default value.

The is specified test is not permitted on a remainder argument.