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From: euaabt@eua.ericsson.se (Anders.Bjornerstedt)
Newsgroups: comp.object,comp.lang.misc,comp.lang.eiffel
Subject: Re: A Hard Problem for Static Type Systems
Message-ID: <1991Apr26.124626.6941@eua.ericsson.se>
Date: 26 Apr 91 12:46:26 GMT
References: <1991Apr20.010347.28984@leland.Stanford.EDU> <1991Apr23.152110.6500@eua.ericsson.se> <1991Apr23.195746.6192@leland.Stanford.EDU>
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craig@elaine35.Stanford.EDU (Craig Chambers) writes:

>In article <1991Apr23.152110.6500@eua.ericsson.se> euaabt@eua.ericsson.se (Anders.Bjornerstedt) writes:
>>I suspect that you could express this, or something very close to it, in 
>>the language CLU. The problem is I dont have the relevant references 
>>accessible, I am short of time, I am lazy, etc etc. So why do I write
>>this ? Well to encourage any person out there knowlegable in CLU to try!

>I used to work with the CLU people and have written a number of CLU
>programs while a student at MIT.  CLU's where clauses provide some of
>the solution (they act like the type patterns I alluded to in an
>earlier message), but CLU has no subtyping, so it can't handle
>comparing subtypes of number.

>-- Craig Chambers

Yes, but CLU does have parameterized types. If I remeber correctly you
could specify the type parameters of a new type by requiring that the
parameter types "conform" by having one or more methods with a certain
signature. This might be more flexible than using inheritance (of 
specification), although less safe since signatures say very little
about semantics. On the other hand maybe the type parameters have to be bound
at compile time in CLU? in which case i guess CLU could not solve the problem.

--------------------------------------------
Anders Bjornerstedt
Software Development Environments
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E-mail: Anders.Bjornerstedt@eua.ericsson.se