using dictionaries
examples
- browser cache: URLs to cached web pages
- email client: aliases to email addresses
- file directory: file name to file contents
dictionary packages
- many programming languages provide built-in support for dictionary-like objects
- Java’s util package has a dictionary class with several implementations, such as hash table
- Scheme has some built-in procedures for handling association lists
assq : Key x List (Pair (Key, Val)) –> Pair (Key, Val)
(define al ‘(a.1 b.2 c.3))
(assq ‘b al) ==> a.1