Soft Typing for Scheme

To: types@dcs.gla.ac.uk
Subject: Soft Typing for Scheme
From: Andrew Wright <wright@cs.rice.edu>
Date: Fri, 17 Dec 93 10:10:59 CST
Approved: types@dcs.gla.ac.uk


I am pleased to announce the first public release of Soft Scheme, a
practical *soft* type system for R4RS Scheme.  Also available is Rice
technical report TR93-218 titled "A practical soft type system for
Scheme" by Andrew K. Wright and Robert Cartwright.

Soft Scheme provides the benefits of static typing for dynamically
typed Scheme.  Like a static type checker, a soft type checker infers
types for variables and expressions.  But rather than reject programs
containing untypable fragments, a soft type checker inserts explicit
run-time checks to transform untypable programs to typable form.
These run-time checks indicate potential program errors, enabling
programmers to detect errors prior to program execution.  Soft type
checking minimizes the number of run-time checks in the compiled code,
enabling dynamically typed languages to attain the efficiency of
statically typed languages like ML.

Soft Scheme is available by anonymous FTP from titan.cs.rice.edu
(128.42.1.30) in file "public/wright/softscheme.tar.Z".  Be sure to
set type binary when transferring this compressed file.  This package
includes the above-mentioned technical report.  The tech report is
also available separately in "public/languages/tr93-218.[dvi,ps].Z".
Soft Scheme relies on my pattern matching extensions to scheme, which
are available in file "public/wright/match.tar.Z".  Obtain both
"softscheme.tar.Z" and "match.tar.Z" if you are interested in running
the system, otherwise just get "tr93-218.[dvi.ps].Z".

Soft Scheme has been tested with Chez Scheme and SCM.  It should port
easily to other Scheme systems with SLIB.  But note that this program
requires a reasonably high performance Scheme system.

Questions and comments welcome!

Andrew Wright