From 814ce2d672d95d0ec0d323fe072c28eddae3faa8 Mon Sep 17 00:00:00 2001
From: Markus Triska <triska@metalevel.at>
Date: Wed, 12 Jul 2023 07:26:52 +0200
Subject: [PATCH] ENHANCED: improved determinism of member/2

Example:

    ?- member(X, "abc").
    %@    X = a
    %@ ;  X = b
    %@ ;  X = c.

This addresses #750.
---
 src/lib/lists.pl | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/lib/lists.pl b/src/lib/lists.pl
index 815e2b2a..8a94ed6a 100644
--- a/src/lib/lists.pl
+++ b/src/lib/lists.pl
@@ -122,8 +122,13 @@ length_addendum([_|Xs], N, M) :-
 %    X = h
 % ;  ... .
 % ```
-member(X, [X|_]).
-member(X, [_|Xs]) :- member(X, Xs).
+
+member(X, [L|Ls]) :-
+        member_(Ls, L, X).
+
+member_(_, X, X).
+member_([L|Ls], _, X) :-
+        member_(Ls, L, X).
 
 %% select(X, Xs0, Xs1).
 %
-- 
2.54.0