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From: peter@yetti.UUCP (Runge)
Newsgroups: net.ai
Subject: Re: Re: Program Specification Languages
Message-ID: <255@yetti.UUCP>
Date: Fri, 13-Sep-85 15:14:03 EDT
Article-I.D.: yetti.255
Posted: Fri Sep 13 15:14:03 1985
Date-Received: Fri, 13-Sep-85 17:27:22 EDT
References: <638@wdl1.UUCP> <629@mmintl.UUCP> <328@chalmers.UUCP>
Organization: York University Computer Science
Lines: 34

> In article <629@mmintl.UUCP> franka@mmintl.UUCP (Frank Adams) writes:
> >
> >The whole idea of a specification language for a computer program is flawed.
> >If the specification is good enough to really determine what the program
> >does, it IS a program; only the compiler is missing.
> 
> Not so. Many precise specifications aren't programs in any sense - the
> simplest example is the integer square root function, specified by
> 
> 	sqrt(n)*sqrt(n) = n & sqrt(n)>=0

I think there are probably some good arguments (but not many) for distinguishing
between specification and programming languages but 
Chalmer's "simplest" example of a specification which is not in "any sense" a
program is quite unconvincing.  Specifications must be taken relative to what
is assumed to be already specified.  In this case, if we assume an appropriate
product relation is available, Chalmer's example becomes a perfectly meaningful
program.  In a logic-programming environment, there is no reason why
	sqrt(X,N) if N > 0 and product(N,N,X)
cannot evaluate N given a value for X, assuming of course that product(X,Y,Z)
can be so specified that its implementation terminates when only Z is
instantiated, or if lazy evaluation is available that an appropriate stream
of bindings for X and Y is generated.  The moral, I think, is that one should
try to be as open-minded as possible as to what could constitute a program,
and avoid the sterile preconceptions which result from our unfortunate
education with conventional programming languages.
-- 

   Peter H. Roosen-Runge, Department of Computer Science, York University
                          Toronto M3J 1P3 , Ontario, Canada
_____________________________________________________________________________
"Eccles, is the ship sinking?"   "Only below the sea."  
"We must try to save the ship -- help me get it into the lifeboat."
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