如何在 SWI-Prolog 的所有统一中启用发生检查? [英] How to enable the occurs check in all unifications in SWI-Prolog?

问题描述

根据维基百科:

为所有统一提供声音统一的实现是 Qu-Prolog 和 Strawberry Prolog，以及(可选地，通过运行时标志):XSB、SWI-Prolog 和 Tau Prolog.

Implementations offering sound unification for all unifications are Qu-Prolog and Strawberry Prolog and (optionally, via a runtime flag): XSB, SWI-Prolog and Tau Prolog.

但是，当我执行 apropos(occur) 时，它只找到 unify_with_occurs_check/2.man 页面没有提到发生"任何一个.如何在 SWI-Prolog 中为所有统一启用发生检查?

However, when I do apropos(occur) it only finds unify_with_occurs_check/2. The man page doesn't mention "occur" either. How can the occurs check be enabled for all unifications in SWI-Prolog?

推荐答案

在 Environment Control，它列出了系统的标志.occurs_check 标志是控制发生统一检查的标志.

In the section on Environment Control, it lists the flags of the system. The occurs_check flag is the one that controls occurs checks for unification.

您可以通过以下方式设置标志:

You can set the flag with:

:- set_prolog_flag(occurs_check, true).

例如:

?- X = f(X).
X = f(X).

?- set_prolog_flag(occurs_check, true).
true.

?- X = f(X).
false.

所以首先它统一了 X 和 f(X).如果我们稍后将 occurs_check 设置为 true，那么如果我们再次尝试将 X 与 f(X) 统一，它失败了.

So first it unifies X with f(X). If we later set the occurs_check to true, then if we try to unify X again with f(X), it fails.

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