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From: zrm@prism.UUCP
Newsgroups: net.ai
Subject: Re: Lisp Machines
Message-ID: <900004@prism.UUCP>
Date: Mon, 27-May-85 21:26:00 EDT
Article-I.D.: prism.900004
Posted: Mon May 27 21:26:00 1985
Date-Received: Fri, 31-May-85 23:56:51 EDT
References: <922@noscvax.UUCP>
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Nf-ID: #R:noscvax:-92200:prism:900004:000:1062
Nf-From: prism!zrm    May 27 21:26:00 1985


Not  only  does  runtime  type-tagging  mean that  errors are detected
earlier than in systems that can't or don't  do runtime type-checking,
it also means that an add instruction  does not  need to  know what it
will  be  adding  together at  compile time.   Doing  type checking in
macro-code is one reason why object oriented  systems run not-so-fast.
If  the  hardware  does  it  for  you  you  spend  less  time fetching
flag-words that tell you what you are trying to  operate on.   It also
makes "hidden" pointers possible, and that lets you pack a list into a
vector.  

In short, hardware support lets languages like Zetalisp deliver on the
promise of high-level-languages:  you are  free to  use the convenient
contructs  of object  oriented without  incurring horrible performance
penalties.  

The huge amount of code that exists for the Zetalisp environment means
that in practical terms, Lisp machines do make programmers
significantly more productive than do Lisp environments and other more
conventional environments found on conventional minis.