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From: Mild Shock <janburse@fastmail.fm>
Newsgroups: comp.lang.prolog
Subject: Re: DCG restrictions on the left-hand side [Novacore]
Date: Tue, 30 Jul 2024 20:45:33 +0200
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This was discussed here:

Definite Clause Grammars Harmonization Proposal
Last edit jschimpf? October 20, 2016, at 12:42 AM
https://eclipseclp.org/wiki/Prolog/DCG

Not sure why Scryer Prolog doesn't implement it.

Mild Shock schrieb:
> 
> In Novacore we are lucky, its a side effect of
> phrase translating the head and a multi-file check:
> 
> ?- [user].
> p;q --> r.
> Fehler: Kann Prädikat ;/2 nicht umdefinieren, nicht als Mehrdateien 
> markiert.
> 
> But might work out differently if a DCG is expanded
> and asserted. Ok, its actually not so bad:
> 
> ?- expand_term((p;q --> r), X), assertz(X).
> Fehler: Kann Prädikat ;/2 nicht aktualisieren.
>      user auf 1
> 
> 
> Mild Shock schrieb:
>> Guess how many newer Prolog systems allow this here:
>>
>> ?- [user].
>> p;q --> r.
>>     true.
>>
>> On the other hand SWI-Prolog disallows it:
>>
>> ?- [user].
>> p;q --> r.
>>
>> ERROR: user://1:29:
>> ERROR:    No permission to define dcg_nonterminal `p;q'
>