Handout 8

Overview

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When shift() is given without an argument in a subroutine, it automatically takes the special array variable @_ as an argument. That special variable is roughly analogous to @ARGV, but at the level of a subroutine: all the arguments given to a subroutine are elements in that arrray. They can be called directly, rather than by using shift() (example).
Returning an argument allows your subroutine to spit out something, like a number or string. You simply use the return() command in the last line of the subroutine (example).
There are three arguments for using subroutines. First, if some command or sequence of commands is repeated, use a subroutine to eliminate the redundancy. Second, you can use subroutines to show the logical structure of your code. If some sequence of commands is a conceptual unit, put it in a separate subroutine.
The third argument is that with subroutines, you can create recursive functions (example. (Using factorials here may seem excessively mathmatical, but if you're familiar with Optimality Theory, then you know about factorial typology....)