From 83a3c52a7513f6cca322707f35a5abe3db9d5018 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?V=C3=ADtor=20Santos=20Costa?= <vsc@dcc.fc.up.pt>
Date: Tue, 15 Dec 2015 09:05:24 +0000
Subject: [PATCH] move length to lists

---
 pl/lists.yap | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 pl/sort.yap  | 41 -----------------------------------------
 2 files changed, 52 insertions(+), 41 deletions(-)

diff --git a/pl/lists.yap b/pl/lists.yap
index a6fce74ab..ea0e69657 100644
--- a/pl/lists.yap
+++ b/pl/lists.yap
@@ -1,3 +1,13 @@
+/**
+ * @file   pl/lists.yap
+ * @author VITOR SANTOS COSTA <vsc@VITORs-MBP.lan>
+ * @date   Thu Nov 19 09:54:00 2015
+ * 
+ * @brief  core lisy operations
+ * 
+ * @ingroup lists
+ * @{
+*/
 
 :- system_module( '$_lists', [], []).
 
@@ -88,4 +98,46 @@ lists:delete([Head|List], Elem, [Head|Residue]) :-
 
 :- set_prolog_flag(source, false). % disable source.
 
+
+
+%   length of a list.
+
+/** @pred  length(? _L_,? _S_)
+
+
+Unify the well-defined list  _L_ with its length. The procedure can
+be used to find the length of a pre-defined list, or to build a list
+of length  _S_.
+
+*/
+
+prolog:length(L, M) :-
+    '$skip_list'(L, M, M0, R),
+	  ( var(R) -> '$$_length'(R, M, M0) ;
+           R == []
+         ).
+
 %
+% in case A1 is unbound or a difference list, things get tricky
+%
+'$$_length'(R, M, M0) :-
+	( var(M) -> '$$_length1'(R,M,M0)
+	; M >= M0 -> '$$_length2'(R,M,M0) ).
+
+%
+% Size is unbound, generate lists
+%
+'$$_length1'([], M, M).
+'$$_length1'([_|L], O, N) :-
+	M is N + 1,
+	'$$_length1'(L, O, M).
+
+%
+% Size is bound, generate single list
+%
+'$$_length2'(NL, O, N) :-
+	( N =:= O -> NL = [];
+          M is N + 1, NL  = [_|L], '$$_length2'(L, O, M) ).
+
+%% @}
+
diff --git a/pl/sort.yap b/pl/sort.yap
index 908c21009..8fcce79b5 100644
--- a/pl/sort.yap
+++ b/pl/sort.yap
@@ -37,47 +37,6 @@
 
 */
 
-%   length of a list.
-
-/** @pred  length(? _L_,? _S_)
-
-
-Unify the well-defined list  _L_ with its length. The procedure can
-be used to find the length of a pre-defined list, or to build a list
-of length  _S_.
-
-
-
-
- */
-length(L, M) :-
-	  '$skip_list'(L, M, M0, R),
-	  ( var(R) -> '$$_length'(R, M, M0) ;
-           R == []
-         ).
-
-%
-% in case A1 is unbound or a difference list, things get tricky
-%
-'$$_length'(R, M, M0) :-
-	( var(M) -> '$$_length1'(R,M,M0)
-	; M >= M0 -> '$$_length2'(R,M,M0) ).
-
-%
-% Size is unbound, generate lists
-%
-'$$_length1'([], M, M).
-'$$_length1'([_|L], O, N) :-
-	M is N + 1,
-	'$$_length1'(L, O, M).
-
-%
-% Size is bound, generate single list
-%
-'$$_length2'(NL, O, N) :-
-	( N =:= O -> NL = [];
-          M is N + 1, NL  = [_|L], '$$_length2'(L, O, M) ).
-
 /** @pred  sort(+ _L_,- _S_) is iso