Re: Dollar sign.

See

http://www.swi-prolog.org/pldoc/doc_for?object=section%28%27sec:topvars%27%29

	--- Jan

On 01/29/2014 09:58 AM, Antoniotti Marco wrote:
>
> On Jan 29, 2014, at 02:27 , Matthew Versaggi <[email protected]<mailto:[email protected]>> wrote:
>
> The "=" sign is the instantiation symbol which binds together (in the prolog sense) the (complex) term $(foo) with the variable X.
> That in a very real sense means that X has become equal to $(foo) in the prolog sense of equal which can be tested using the '==' predicate (if I remember correctly).
>
> $(foo) = X.
> X = $foo.
>
> Yes.  I know about =, == and unification.  The question is about the ‘$’ sign.  I would have expected the above to yield
>
> ?- $(foo) = X.
> X = $(foo)
>
> It doesn’t.
>
> Also note that:
>
> ?- compound($(x, y)).
> true.
>
> ?- compound($(foo)).
> true.
>
> ?- compound($foo).
> true.
>
> So.  What is going on with the ‘$’ sign/predicate?
>
> I am just being lazy and I admit it.  Where is the use of ‘$’ as a predicate/operator explained in the manual (as I said, I am lazy and I gave up searching) :) :)
>
> Cheers
> —
> MA
>
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> On Tue, Jan 28, 2014 at 6:44 PM, Antoniotti Marco <[email protected]<mailto:[email protected]>> wrote:
> Hi
>
> Apologies for the stupid question.  I must be missing something with the dollar sign.  I don’t quite understand what is going on in the following transcript.
>
>
> ?- $(foo) = X.
> X = $foo.
>
> ?- $(foo, bar) = X.
> X = $(foo, bar).
>
> ?- X = foo, $X.
> ERROR: toplevel: Undefined procedure: ($)/2 (DWIM could not correct goal)
> ?- X = foo, $(X).
> ERROR: toplevel: Undefined procedure: ($)/2 (DWIM could not correct goal)
> ?- X = foo, $(X, zot).
> ERROR: toplevel: Undefined procedure: ($)/2 (DWIM could not correct goal)
> ?- X = foo, $(zot, X).
> ERROR: toplevel: Undefined procedure: ($)/2 (DWIM could not correct goal)
> ?- $(foo, bar) = X.
> X = $(foo, bar).
>
> Does anybody have quick explanation about this?
>
> Thanks
>
>
> --
> Marco Antoniotti, Associate Professor tel. +39 - 02 64 48 79 01
> DISCo, Università Milano Bicocca U14 2043 http://bimib.disco.unimib.it
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> Marco Antoniotti, Associate Professor tel. +39 - 02 64 48 79 01
> DISCo, Università Milano Bicocca U14 2043 http://bimib.disco.unimib.it
> Viale Sarca 336
> I-20126 Milan (MI) ITALY
>
> Please note that I am not checking my Spam-box anymore.
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