1 + length( all but the first character of the tail )

Recursive Definition of String Length

Keep doing this until there are no characters in the tail. The tail of a string that contains one character is the empty string.

The length of a string is:

1. If a string has no characters, then its length is 0.
2. Otherwise,
   • the length of the string is 1 + length of the tail

This looks a lot like the "crossing the parking lot" procedure in chapter 90.