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From: boehm@parc.xerox.com (Hans Boehm)
Newsgroups: comp.object,comp.lang.misc,comp.lang.eiffel
Subject: Re: A Hard Problem for Static Type Systems
Message-ID: <boehm.672358774@siria>
Date: 22 Apr 91 22:19:34 GMT
References: <1991Apr20.010347.28984@leland.Stanford.EDU>
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Aside from syntactic issues, this doesn't seem very hard in languages like
Russell, Quest, or Poly.  I either need a built-in type number, or I need
to explicitly define something that is the tagged union of integers and floats.
(The tag may be a method suite.) I then define min to take a type (or algebra,
or your favorite term...) with a "<" operation and its two "real" arguments.
(When I apply min, the type argument can be inferred.)  This forces a static
check that the two argument types are the same.

This still involves at least some dynamic method selection.  But that seems
inherent in the problem.

Whether you consider these languages to be practical is a matter of taste.
They have all been used to build nontrivial programs.

Hans