🚀 go-pugleaf

I wanted to discuss the actually rather vague term "declarative",
to make the point that this term should perhaps be avoided.

I don't assume that something that is "declarative", a priori is
"finer" than anything else. The unclarity has to do with which
objects you attribute the property "declarative" to (is it a program,
a specification, a programming language or a programming style or
something else ?). Lloyd in his book "The foundation of logic
programming" talks about "the declarative concept of finite failure"
which indicates that concepts can be declarative, etc. 

Since "declarative" is a property attributed to programming languages
I would like to make the point that we could consider a FORTRAN
program as a syntactic sugar for a sequence of transition relations
which when satisfied by a theorem prover represents the execution of
the FORTRAN program, and thereby FORTRAN should be a "declarative"
language.  The "declarative reading" of some PROLOG programs is well
defined in terms of least Herbrand models, of course, even though its
practical use is more limited than we sometimes claim, since most
PROLOG programming involves coding which sometimes adds meaning
to the program that the PROLOG theorem prover cannot deduce if
goal order is reversed etc.

I would like to point out in contrast to some other comments on my
posting that many normal uses of 'cut' does NOT cause a problem for
the "declarative" reading of a Horn clause program as a set of axioms.
It just affects the completeness in that some solutions are not found.

In <517@quintus.UUCP> ROK writes:
>In article <ALF.88Oct2184429@hathor.sics.se> alf@sics.se (Thomas Sj|land) writes:
>>Statement 2, (viewpoint held by some experts who agree to statement 1):
>>	 "functional languages are NOT declarative, while logic programming
>>	  and equational languages are if they have completeness"
>
>Please name these experts, so that I will know whose books to avoid!

This opinion was stated by some of my colleagues over dinner, and it
may not be as silly as it looks. You can view "declarative programming"
as meaning "programming with axioms and a theorem prover". If you see
a pure functional program as syntactic sugar for a lambda expression,
I guess it makes sense to say that the functional program is not 
"declarative", simply since a lambda expression is not an axiom 
in a theory. Another reading of a functional program could be that
it is a way of defining a directed relation, whereby it suddenly becomes 
"declarative". Well... let's just avoid the term "declarative" when we
try to describe properties of languages like Prolog, shall we ? 

I shouldn't have brought this up in the first place. We all know what we
are talking about anyway.






--
Thomas Sj|land
SICS, PO Box 1263, S-164 28 KISTA, SWEDEN
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Internet: alf@sics.se or {mcvax,munnari,ukc,unido}!enea!sics.se!alf