[Cst-1b] Mistake in Prolog Notes?

[Matthew Parkinson]

If you run the following code:

isItThis([[a,b],c]).
isItThat(.(.(a,.(b,[])),.(c,[]))).

?-isItThis(.(.(a,.(b,[])),.(c,[]))).
?-isItThat([[a,b],c]).

You get yes for both. Proving equivalence
As on the previous page he has [[the,cat],sat] as an example of a list I would
say it is most definately a list.

Matthew

Kevin Chan wrote:

> Mo
>
> I think the point is that in dot notation the tail needs to be a list of
> whatever the head is hence if the head is a list as it is in the example
> then the tail must be a list of lists.  In the example the tail is a simple
> list and hence it doesn't conform to the rules for a list
>
> That is what I think anyways
>
> Kev
>
> ----- Original Message -----
> From: M.Y.W.Y.B. <mywyb2@hermes.cam.ac.uk>
> To: CST 1b Revision List <cst-1b@srcf.ucam.org>
> Sent: Wednesday, May 17, 2000 10:00 PM
> Subject: Re: [Cst-1b] Mistake in Prolog Notes?
>
> > --On Mittwoch, 17. Mai 2000, 21:37 +0100 "Nic Infante"
> > <ngli2@thor.cam.ac.uk> wrote:
> >
> > > I think it's not a proper list as the first term [a,b] is a list and
> > > the second c (an atom since in lower case) is not. notation, the second
> > > term . In the dot notation, (c,[]) would have to be a list of lists,
> which
> > > it can't be.  [[a,b],C] could be a list since C is a variable and could
> be
> > > instantiated to a list. Although I've just noticed that he's got
> > > [[the,cat],sat] as an example of a list so I'm not sure.
> >
> > In Prolog list elements needn't have the same type (unlike ML).
> >
> > So
> > [ 3.14, apple, [1], (a,b) ]
> > is a proper list.
> >
> > Therefore if you've got the term .(X,Y), the necessary and sufficient
> > condition for it being a proper list is that Y has to be a proper list of
> > length >= 0.
> > In the example, Y corresponds to .(c,[]) which clearly is a list.
> >
> > Moritz
> >
> >
> >
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