A new functional database language called PFL is described.  PFL is a lazy
functional language with a polymorphic type inference system which enforces
strong static type-checking.  All functions persist in a repository, and are
specified by the insertion and deletion of equations.  New data types can be
added at any time, and the order in which types and equations are inserted
is immaterial.  A class of functions called selectors are used for the
storage of bulk data.  Selectors allow flexible, efficient access to stored
data and encourage a natural and succinct programming style.  <P>

In Section 1 of the paper we describe the PFL type system, and in Section 2
the definition of functions.  In Section 3 we describe selector functions.
Section 4 describes the evaluation of queries, Section 5 the deletion of
equations and type information, and Section 6 the retrieval of metadata.  In
Section 7 we illustrate the features of PFL, and compare PFL with other
languages.  An extended example, based upon the manufacturing company parts
database example is presented in Section 8.