Polymorphic Type-Checking in Scheme
		
				by
		Steven Jenkins and Gary T. Leavens

		       	     Abstract

This paper presents a type-inference system for Scheme that is designed to 
be used by students in an introductory programming course.  The major goal 
of the work is to present a simple type inference system that can be used 
by beginning students, yet is powerful enough to express the ideas of 
types, polymorphism, abstract data types, and higher-order procedures.  
The system also performs some rudimentary syntax checking.  The system 
uses subtyping, but only in a primitive fashion.  It has a type datum which 
is a supertype of all types, and a type poof which is a subtype of all types.  
It uses and-types (intersection types) to control the use of datum and to 
generate accurate but simple types.

Keywords: abstract data type, type inference

1995 CR Categories:
D.3.3 [Programming Languages]
	Language Constructs -- Abstract data types, data types and structures
D.3.4 [Programming Languages]
	Processors --- preprocessors
F.3.3 [Logics and Meanings of Programs]
	Studies of Program Constructs --- type structure.