Association structures

A variety of data structures can be described as associations of values to places:

• Records: have a finite collection of places. For example, colors have :red, :green, and :blue places.
• Lists: have an infinite and enumerated set of places. The places in lists and vectors are enumerated by the nth function.
• Hashes: may have anything, even other hashes, as places.

Lists and hashes can both be generalized to container types because unlike records they contain an infinite number of places.