Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!news.cs.indiana.edu!chaynes@sunfish.cs.indiana.edu
From: chaynes@sunfish.cs.indiana.edu (Chris Haynes)
Newsgroups: comp.lang.scheme
Subject: Re: ML-like type-checker for Scheme subset?
Message-ID: <1991May13.162700.3072@news.cs.indiana.edu>
Date: 13 May 91 21:26:34 GMT
References: <5710@goanna.cs.rmit.oz.au>
Organization: Computer Science, Indiana University, Bloomington.
Lines: 23


    It occurred to me that static type checking could be introduced _after_
    the other concepts have been presented, and that an ML-style type checker
    would suit Scheme rather well.  There are a handful of functions like memq
    which would require union types, but well-typed replacements are easy to
    define.

    Has anyone already done this?  I _could_ write the code myself, but it
    would be a pity to re-invent the wheel.

With the help of a student, Hsianlin Dzeng, I have done this.  The
resulting typed dialect of Scheme is called Infer.  It supports most
features of the ML type system, less modules, plus a few additional
features.  I'm pleased with the result, and it has already proved useful at
Indiana University in denotational semantics and types courses.  It may
someday be used in introductory courses as well, but not until it's been
developed further and tutorial material has been written.  Currently the
implementation (about 40 pages of Infer code) still has a lot of rough
edges and I've got fair sized list of features I'd like to add.  My hope is
to contribute a version to the Scheme yellow pages for general use next
spring.

Chris Haynes