2	Copyright 2012-2015 Samer Abdallah (Queen Mary University of London; UCL)
    4	This program is free software; you can redistribute it and/or
    5	modify it under the terms of the GNU Lesser General Public License
    6	as published by the Free Software Foundation; either version 2
    7	of the License, or (at your option) any later version.
   10	This program is distributed in the hope that it will be useful,
   13	but WITHOUT ANY WARRANTY; without even the implied warranty of
   15	GNU Lesser General Public License for more details.
   17	You should have received a copy of the GNU Lesser General Public
   18	License along with this library; if not, write to the Free Software
   19	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
   22:- module(listutils,
   23	[	natural/1		% test or enumerate natural numbers
   24	,	int/1				% test or enumerate integers
   25   ,  enumerate/2    % pair list items with 1-based positon
   26   ,  measure/2      % list with same length list of naturals
   27	,	take/3, takec/3, take_while/3
   28	,	drop/3, dropc/3, drop_while/3
   29   ,  map_filter/3
   30   ,  foldr/4
   31   ,  split_at/4
   32   ,  same_length/2
   33	,  rep/3          % make a list of repeats of the same term
   34	,  cons/3         % list constructror
   35	,	decons/3       % list deconstructor
   36	,	print_list/1	% writes each element on a new line
   37	,	printq_list/1	% as print_list but quotes atom as necessary
   38	,	print_numbered_list/1
   39   ,  zip/3
   40	]).   41
   42:- meta_predicate
   43		drop_while(1,?,?)
   44	,	take_while(1,?,?)
   45   ,  map_filter(2,+,-)
   46   ,  foldr(3,?,?,?)
 natural(+N) is semidet
natural(-N:natural) is multi
Means N is a natural number (includes 0). If N is a variable, succeeds an infinite number of times on backtracking, returning all natural numbers.
   55natural(N) :- (var(N) -> between(0,inf,N); integer(N), N>=0).
 int(+N) is semidet
int(-N:integer) is multi
Means N is an integer. If N is a variable, succeeds an infinite number of times on backtracking, returning all integers starting at zero and interleaving positive and negative values.
   65int(N)     :- nonvar(N), integer(N).
   66int(N)     :- var(N), (N=0; (between(1,inf,M), (N=M; N is -M))).
 enumerate(+L:list(A), -NL:list(pair(natural,A))) is det
enumerate(-L:list(A), -NL:list(pair(natural,A))) is nondet
   71enumerate(X,Y) :- enumerate(X,0,Y).
   73enumerate([X|Xs],I,[J-X|IXs]) :- J is I+1, enumerate(Xs,J,IXs).
 measure(+L:list(_), -N:list(natural)) is det
measure(-L:list(_), -N:list(natural)) is nondet
True when L and N are the same lenght and N is a sequence of integers starting at 1.
   78measure(Xs,Ns) :- measure(Xs,Ns,0).
   80measure([_|Xs],[N|Ns],N) :- M is N+1, measure(Xs,Ns,M).
 print_list(+L:list) is det
Print a list, one item per line.
   85print_list([]) :- writeln('~'), nl.
   86print_list([H|T]) :- print(H), nl, print_list(T).
 printq_list(+L:list) is det
Print a list, one item per line, as with writeq/1.
   91printq_list([]) :- writeln('~'), nl.
   92printq_list([H|T]) :- writeq(H), nl, printq_list(T).
 print_numbered_list(+L:list) is det
Print a list with numbered lines.
   97print_numbered_list(L) :-
   98	length(L,Max),
   99	number_codes(Max,MC),
  100	length(MC,Width),
  101	print_num_list(Width,1,L).
  103print_num_list(_,_,[]) :- nl.
  104print_num_list(Width,N,[H|T]) :- succ(N,M),
  105	copy_term(H,H1),
  106	numbervars(H1,0,_),
  107   format('~` t~d~*+. ~q\n',[N,Width,H1]),
  108	print_num_list(Width,M,T).
  110% padleft(_,W,In,In) :- length(In,W).
  111% padleft(P,W,In,[P|Out]) :- succ(V,W), padleft(P,V,In,Out).
 cons(?Head:A, ?Tail:list(A), ?List:list(A)) is det
List constructor.
 decons(?Head:A, ?List:list(A), ?Tail:list(A)) is det
List deconstructor.
 rep(+N:natural, ?X:A, -L:list(A)) is det
rep(-N:natural, ?X:A, -L:list(A)) is multi
Make a list consisting of N repeats of the same term. If called with N unbount, creates progressively longer and longer lists on backtracking.
  129rep(N,A,[A|X]) :-
  130	(	nonvar(N)
  131	-> succ(M,N), rep(M,A,X)
  132	; rep(M,A,X), succ(M,N)
  133	).
 drop(+N:natural, +In:list(A), -Out:list(A)) is semidet
True if removing exactly N elements from the head of In results in Out. Fails if there are fewer than N elements in In.
  138drop(N,X,T) :- length(H,N), append(H,T,X).
 take(+N:natural, +In:list(A), -Out:list(A)) is semidet
True when Out consists of the first N elements of Out. Fails if In contains fewer than N elements.
  143take(N,X,H) :- length(H,N), append(H,_,X).
 dropc(+N:natural, +In:list(A), -Out:list(A)) is det
Unifies Out with the result of removing N elements from the head if In, or the empty list if In has fewer than N elements. (The 'c' is for a 'complete' as opposed to a 'partial' function.)
  149dropc(0,T,T) :- !.
  150dropc(N,[_|T],V) :- !, succ(M,N), dropc(M,T,V).
 takec(+N:natural, +In:list(A), -Out:list(A)) is semidet
Unifies Out with the first N elements of In, or the empty list if In has fewer than N elements. (The 'c' is for a 'complete' as opposed to a 'partial' function.)
  157takec(0,_,[]) :- !.
  158takec(_,[],[]) :- !.
  159takec(N,[X|XS],[X|YS]) :- succ(M,N), takec(M,XS,YS).
 drop_while(+P:pred(A), +In:list(A), -Out:list(A)) is det
Remove all elements from head of In that are accepted by P and return the remained in Out.
  165drop_while(P,[X|T],V) :- call(P,X) -> drop_while(P,T,V); V=[X|T].
 take_while(+P:pred(A), +In:list(A), -Out:list(A)) is det
Remove all elements from head of In that are accepted by P and return them in Out.
  173take_while(P,[X|T],O) :- call(P,X) -> O=[X|V], take_while(P,T,V); O=[].
 split_at(+N:natural, -Prefix:list(A), -Suffix:list(A), +In:list(A)) is det
split_at(-N:natural, -Prefix:list(A), -Suffix:list(A), +In:list(A)) is det
True when Prefix is the length-N prefix of Items and Suffix is the list of remaining items. Also works in other modes, like append.
  182split_at(N,Pref,Rest,List) :-
  183   (  nonvar(N)
  184   -> length(Pref,N), append(Pref,Rest,List)
  185   ;  append(Pref,Rest,List), length(Pref,N)
  186   ).
 same_length(+L1:list(_), +L2:list(_)) is det
same_length(-L1:list(_), -L2:list(_)) is nondet
True when L1 and L2 are lists of the same length.
  193same_length([_|X],[_|Y]) :- same_length(X,Y).
 zip(+X:list(A), +Y:list(B), -Z:list(pair(A,B))) is det
zip(-X:list(A), -Y:list(B), +Z:list(pair(A,B))) is det
zip(?X:list(A), ?Y:list(B), ?Z:list(pair(A,B))) is nondet
True when Z is the list of pairs formed from corresponding elements of X and Y. The pair type is pair(A,B) ---> A-B.
  202zip([X|XX],[Y|YY],[Z|ZZ]) :- Z=X-Y, zip(XX,YY,ZZ).
 map_filter(+P:pred(+A,-B), +L1:list(A), -L2:list(B)) is det
Like maplist/3, but filtering out those elements of L2 for which P fails.
  206map_filter(P,L1,L2) :- map_filter_(L1,L2,P).
  207map_filter_([], [], _).
  208map_filter_([X|Xs], [Y|Ys], P) :- call(P,X,Y), !, map_filter_(Xs, Ys, P).
  209map_filter_([_|Xs], Ys, P) :- map_filter_(Xs, Ys, P).
 foldr(P:pred(A,B,B), X:list(A), S1:B, S2:B) is det
  212foldr(P,XX) --> foldr_(XX,P).
  213foldr_([],_) --> [].
  214foldr_([X|XX],P) --> foldr_(XX,P), call(P,X)