A store can be thought of as a region of memory in which objects, known as references, can be dynamically allocated, read, and written. Stores are homogeneous: all references in a store of type 'a store have the content type, namely 'a. In general, a store should be thought of as a mutable object. Some stores support a cheap copy operation, because the underlying data structure allows it: for instance, a store implemented as a reference to a persistent map supports cheap copies. Some stores do not support copy at all: for instance, a store implemented using primitive references does not support copies.

new_store() creates an empty store.

copy s returns a copy of the store s. Every reference that is valid in the store s is also valid in the new store, and has the same content in both stores. The two stores are independent of one another: updating one of them does not affect the other. When supported, copy is cheap: it can be expected to run in constant time. However, some stores does not support copy; in that case, an unspecified exception is raised.

A reference of type 'a rref can be thought of as (a pointer to) an object that exists in some store.

make s v creates a fresh reference in the store s and sets its content to v. It updates the store in place and returns the newly-created reference.

get s x reads the current content of the reference x in the store s. It may update the store in place, and returns the current content of the reference.

set s x v updates the store s so as to set the content of the reference x to v. It updates the store in place.

eq s x y determines whether the references x and y are the same reference. It may update the store in place, and returns a Boolean result. The references x and y must belong to the store s.

Make constructs persistent stores based on immutable integer maps.