From 1ca3670047172610f0c284df5d5171fa840f97ce Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <peter@pmikkelsen.com>
Date: Wed, 30 Jun 2021 23:53:19 +0000
Subject: Add length/2 and member/2

---
 example.pl |  3 ---
 stdlib.pl  | 11 +++++++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/example.pl b/example.pl
index 3df943c..d9e4108 100644
--- a/example.pl
+++ b/example.pl
@@ -24,6 +24,3 @@ tester(A, B) :- true.
 
 =(A,A).
 
-length([], zero).
-length([Head|Tail], suc(Length)) :-
-	length(Tail, Length).
diff --git a/stdlib.pl b/stdlib.pl
index ecf7417..01b3e5f 100644
--- a/stdlib.pl
+++ b/stdlib.pl
@@ -55,3 +55,14 @@ A @>= B :-
 	A == B.
 A @>= B :-
 	A @> B.
+
+% List predicates
+
+length([], 0).
+length([_|Tail], Length) :-
+	length(Tail, Length0),
+	Length is Length + 1.
+
+member(X, [X|_]).
+member(X, [_|Tail]) :-
+	member(X, Tail).
-- 
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