First Class File I/O
Marco Pil

Computing Science Institute, University of Nijmegen,
Postbus 9010, 6500 GL Nijmegen, The Netherlands
e-mail: marcop@cs.kun.nl

Abstract. In most functional languages little attention has been paid
to file I/O. The file system is poorly typed at best and some classes of
objects, in particular functions, cannot be stored on disk at all. In this
article we present a mature type system for typing files. We also discuss
briefly how we plan to implement the storage of functions in files. We
make use of the concept of dynamic types, as introduced in Abadi et
al., which provide an interface between statically and dynamically typed
parts of a program. We have modified the concept of dynamic types to
include polymorphic types in a natural way and we are implementing this
modified system of dynamic types in the functional language Clean. We
have developed a simple run-time matching algorithm for the dynamic
type checks. We present some of the problems we encountered when the
system of dynamic types is implemented to its full extent in a language
that already has an elaborate type system. Finally we show that the
same concepts that we used for constructing the file system can be used
for communication between independently running programs in general.