homework5.pl

%Compresses each sequence of consecutive identical ground terms.
%The first argument may contain consecutive identical terms.
%The second argument contains no consecutive identical terms.
compress([],[]) :- !.
compress([X, X|Xs], [X|Ys]) :- !, compress([X|Xs], [X|Ys]).
compress([X|Xs], [X|Ys]) :- compress(Xs, Ys).

%Flattens a list of lists into a flat list.
%The first argument should be the unflattened list.
%The second argument should be the flattened list.
my_flatten([],[]) :- !.
my_flatten([X|Xs], Ys) :- !, my_flatten(X, Y1), my_flatten(Xs, Y2), append(Y1, Y2, Ys).
my_flatten(X, [X]).

% Creates a list of lists with consecutive repetitions of ground terms.
% The first argument may contain consecutive repetitions.
% The second argument groups the consecutive repetitions into lists and
% returns a list of these lists.
pack([],[]) :- !.
pack([X],[[X]]) :- !.
pack([X, Y|Xs],[[X]|Ys]) :- X\=Y, !, pack([Y|Xs],Ys).
pack([X|Xs],[[X|Y]|Ys]) :- pack(Xs,[Y|Ys]).

%Creates a list of lists counting the number of consecutive repetitions.
%The first argument should be a list with consecutive repetitions.
%The second argument is the list with the count of repetitions.
rlencode([],[]) :- !.
rlencode([X],[Y]) :- pack(X,[[H|Hs]|T]), length([H|Hs],Y1), rlencode(T,Y2),append([H|Y1],Y2,Y).

%Creates the original list from the list of lists produced by rlencode.
%The first argument is a list with the count of repetitions.
%The second argument will be the list with consecutive repetitions.
rldecode([],[]) :- !.
rldecode([[X|1]|Xs],[X|Ys]) :- !, rldecode(Xs, Ys).
rldecode([[X|N]|Xs],[X|Ys]) :- N1 is N-1, rldecode([[X|N1]|Xs],[Ys]), !.
rldecode([X|Xs],[X|Ys]) :- rldecode(Xs, Ys).

%Creates a list of consecutive integers between two bounds.
%The first argument is the lower bound.
%The second argument is the upper bound.
%The third argument is the list of integers.
range(X,X,[X]) :- integer(X), !.
range(X,Y,Z) :- integer(X), integer(Y), !, X1 is X+1, range(X1,Y,W), append([X],W,Z).