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From: johnson@p.cs.uiuc.edu
Newsgroups: comp.lang.smalltalk
Subject: Re: Performance of "doesNotUnderstand:"
Message-ID: <80500071@p.cs.uiuc.edu>
Date: 2 Sep 89 23:03:22 GMT
References: <9070@june.cs.washington.edu>
Lines: 21
Nf-ID: #R:june.cs.washington.edu:9070:p.cs.uiuc.edu:80500071:000:1057
Nf-From: p.cs.uiuc.edu!johnson    Sep  1 13:03:00 1989


The type system that Russ Abbott described is basically the same as
that of Emerald.  There was a paper at OOPSLA 86 about it and some
later papers in IEEE Transactions on Software Engineering.  There
was also a PhD thesis by Norman Hutchinson at the U. of Washington
that described the type system in detail.

A signature based type system will not always work in Smalltalk,
because there are a lot of explicit checks for nil and a few other
explicit checks for the class of objects.  These require a type
system based on discriminated unions.  However, signatures fit in
well with unions.  The type system for Typed Smalltalk uses both.
Discriminated unions are also better for code optimization.

Justin Graver just finished a thesis that describes the type system
for Typed Smalltalk.  The thesis also describes type inference.  The
thesis is still in the process of being copied, but I would be glad to
send anyone a copy if they want it.  The main part of the thesis is
a formal description of the type system, so casual readers beware!

Ralph Johnson