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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 20:43:44 +0200
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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'