An association list is a conventional data structure that is often used
to implement simple key-value databases. It consists of a list of
entries in which each entry is a pair. The key of each entry is
car of the pair and the value of each entry is the
ASSOCIATION LIST ::= '( (KEY1 . VALUE1) (KEY2 . VALUE2) (KEY3 . VALUE3) … )
Association lists are also known, for short, as alists.
The structure of an association list is just one example of the infinite
number of possible structures that can be built using pairs and lists.
As such, the keys and values in an association list can be manipulated
using the general list structure procedures
set-cdr! and so on. However,
because association lists are so useful, Guile also provides specific
procedures for manipulating them.