From: Markus Triska <triska@metalevel.at>
Date: Sun, 18 Jan 2026 08:57:37 +0000 (+0100)
Subject: ADDED: not_si/1
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=0dc94ecc0bf1a40874b844263a48b880e8a596f5;p=scryer-prolog.git

ADDED: not_si/1

For a recent example that would benefit from this, see "Prolog Basics
Explained with Pokémon" by @alexpetros:

    https://unplannedobsolescence.com/blog/prolog-basics-pokemon/

Thank you a lot!
---

diff --git a/src/lib/si.pl b/src/lib/si.pl
index 0e29c190..8a642289 100644
--- a/src/lib/si.pl
+++ b/src/lib/si.pl
@@ -40,6 +40,7 @@
                term_si/1,
                chars_si/1,
                dif_si/2,
+               not_si/1,
                when_si/2]).
 
 :- use_module(library(lists)).
@@ -100,6 +101,17 @@ dif_si(X, Y) :-
    ; throw(error(instantiation_error,dif_si/2))
    ).
 
+%% not_si(+Goal).
+%
+%  True if Goal is not provable. Instantiation error if Goal is not
+%  ground.
+
+:- meta_predicate(not_si(0)).
+
+not_si(Goal) :-
+   term_si(Goal),
+   \+ Goal.
+
 :- meta_predicate(when_si(+, 0)).
 
 %% when_si(Condition, Goal).