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Re: segmentation fault writing cyclic term

From: Daniel Diaz
Subject: Re: segmentation fault writing cyclic term
Date: Fri, 10 Dec 2021 08:49:49 +0100

Hi Paul,

Acyclic terms are not supported but the predicate acyclic_term/1 if provided to 
test if a term is acyclic. You can use it before printing a term.
The top-level does this before printing a solution (else it emits the error 
message you mentioned).


> Le 4 déc. 2021 à 17:55, Paul Eggert <eggert@cs.ucla.edu> a écrit :
> On 12/4/21 03:21, Paulo Moura wrote:
>>> | ?- X = X+1, write(X).
>>> X = X+1, write(X).
>>> Segmentation fault (core dumped)
>>> Shouldn't write/1 be protected against cyclic terms?
>> Note that support for cyclic terms is not a ISO Prolog standard requirement.
> Quite right, this is not a standards violation. Still, gprolog already 
> defends against cyclic terms when it outputs them:
>  | ?- X=X+1.
>  cannot display cyclic term for X
> so presumably it could defend against them in 'write' if this was considered 
> useful (which it would be, for my students...).

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