I/O trees and interactive lazy functional programming

Abstract

Computer programs interact with users, and programmers must describe this interaction when they write programs. Programming languages usually allow programmers to describe this interaction with primitive read and write functions. The situation is not so simple in the realm of lazy functional languages. Because read and write are not referentially transparent, programmers cannot use them in lazy functional languages. This paper shows that lazy programs can interact with users by generating I/O Trees-structures that describe possible interactions between user and program. I/O trees encode a program’s dynamic behavior in static structure. This paper presents the fundamental structure and interpretation of I/O trees, describes extensions to I/O trees, and suggests ways programmers can write programs that generate I/O trees.