Standards questions, from ISO Convener 
Author Message
 Standards questions, from ISO Convener

Roger Scowen, convener and project editor for the ISO Prolog Group
(WG17), had a few comments on the discussion going on here, and gave
me permission to post the nessage below.  In it, Roger cites a number
of ISO documents.  To give a flavour of the documents, here is the
relevant part of N26, pg 9:

Resolution XXX asks the project editors to formulate Principles and
Rationale for Standard Prolog...

        a) Faithful to the spirit of logic programming

        b) The standard shall have a clear unambiguous definition

        c) The standard will try to leave the way open for extensions,
           for example the inclusion of constraints, object-oriented
           programming, parallel programming.

        d) The standard will not incluide features that will be an
           embarrassment in the future because they are expensive to
           those programs that do not use them, and provide only small
           benefits for those that do.

        e) The standard will not provide the same functionality in two
           different ways without good reason.

        f) Standard Prolog will be suitable for the development of large
           programs as well as small ones.

        g) Standard Prolog will, when possible, be compatible with existing

        h) When alternative formulations are possible, the main
         guidelines for the decision must be:  
                1) Reinforce the coherence and clarity of the language
                   if there is no significant cost

                2)  Choose the alternative that reinforces the
                   declarative aspects of Prolog"

Here is Roger's message:
Dear Bernard

I have not seen all the correspondence on arg/3 in comp.lang.prolog
but here a few comments.

WG17 (and BSI) have tried to follow general principles - but have been
unsuccessful in defining them or agreeing on proposals for principles.
For example, see N26,p9; N35,p1; N36,Res'nA44.

I have tried to apply consistently the concepts of Instantiation error
(the goal might succeed or fail if more of the arguments were
instantiated) and Type error (the goal can never succeed because one
argument has an incorrect type).

The idea of instantiation error is to leave open the idea of
coroutining and freeze, etc.

But WG17 has changed its mind on Term ordering - where ordering of
variables used to give an instantiation error, but is now
implementation dependent.

Defining the error cases has always been the most difficult part of
defining a BIP - see my comment in N64,

[This concerns the new I/O predicates.  Without a good set of guiding
principles, Roger cannot decide when a predicate should fail or
generate an error.  Bernard]

Roger Scowen (SC22 WG17 Convener), DITC/93, National Physical Laboratory
Teddington, Middlesex, England   TW11 0LW
24 October 1990
Tel - Britain: 081 943 6956 (If no answer - NPL Operator is 081 977 3222)
Tel - Abroad: +44 81 943 6956 (NPL Operator is +44 81 977 3222)
Telex: 262344
Fax: Britain -  081 977 7091, Abroad -  +44 81 977 7091

                                Bernard Silver
                                GTE Laboratories

                                (617) 466-2663

Tue, 13 Apr 1993 20:15:14 GMT  
 [ 1 post ] 

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