language developed by Carol Small at Birkbeck College, London,
In PFL, functions are defined equationally and bulk data is
stored using a special class of functions called selectors.
new user-defined data types and values. All functions, types
and values persist in a
database. Functions can be written
which update all aspects of the database: by adding data to
selectors, by defining new equations, and by introducing new
data types and values.
whilst updates are referentially opaque and are executed
destructively, all evaluation is referentially transparent.
whilst updates are dynamically type checked at run time,
expressions are type checked before they are evaluated and no
type errors can occur during their evaluation.
C. Small, Information Systems 18(8), 1993, pp. 581-95].
(1995-04-27)