Read_stream_to_codes

Help! Predicate
16

Now that I have a better grasp on how to combine multiple streams (difference list) using EDCG here is the code. As I am not an expert with EDCG this may not be the best way, but it does work.

Click triangle to see example code 
% -----------------------------------------------------------------------------

:- module(edcg_example,
    [
        dl_append_edcg/6
    ]).

% -----------------------------------------------------------------------------

:- use_module(library(edcg)).

% -----------------------------------------------------------------------------

% These are just two versions of the classic difference list append.
% These are here  for use with the test cases to show that these and the EDCG
% version all pass the same test cases.

dl_append_expanded(Source_1,Hole_1,Source_2,Hole_2,Destination,Destination_hole) :-
    Destination = Source_1,
    Hole_1 = Source_2,
    Hole_2 = Destination_hole.

dl_append(Source_1,Source_2,Source_2,Hole_2,Source_1,Hole_2).

% -----------------------------------------------------------------------------

edcg:acc_info(source_1, Destination, Source_1, _Hole_1, Destination = Source_1).
edcg:acc_info(source_2, Hole_1, Source_2, _Hole_2, Hole_1 = Source_2).
edcg:acc_info(destination, Hole_2, _Destination, Destination_hole, Hole_2 = Destination_hole).

edcg:pred_info(dl_append_edcg,0,[source_1,source_2,destination]).

% NB Originally tried using EDCG notation Destination/destination/Hole_2 which failed miserably.

dl_append_edcg -->>
    Destination/destination,   % Set (unify) start of difference list
    [Destination]:source_1,    % Set (unify) hole of difference list
    Hole_1/source_1,
    [Hole_1]:source_2,
    Hole_2/source_2,
    [Hole_2]:destination.

% ?- listing(dl_append_edcg/6).
% edcg_example:dl_append_edcg(A,
%                             Hole_1,
%                             B,
%                             Hole_2,
%                             Destination,
%                             C) :-
%     true,
%     Destination=A,
%     true,
%     true,
%     Hole_1=B,
%     true,
%     true,
%     Hole_2=C,
%     true.

% Refined variable names by hand
%
% edcg_example:dl_append_edcg(Source_1,
%                             Hole_1,
%                             Source_2,
%                             Hole_2,
%                             Destination,
%                             Destination_hole) :-
%     true,
%     Destination=Source_1,
%     true,
%     true,
%     Hole_1=Source_2,
%     true,
%     true,
%     Hole_2=Destination_hole,
%     true.

% Refined variable names by hand
% Removed true statements
%
% edcg_example:dl_append_edcg(Source_1,
%                             Hole_1,
%                             Source_2,
%                             Hole_2,
%                             Destination,
%                             Destination_hole) :-
%     Destination=Source_1,
%     Hole_1=Source_2,
%     Hole_2=Destination_hole.

% Refined variable names by hand
% Removed true statements
% Refactored unification into head
%
% edcg_example:dl_append_edcg(Source_1, Source_2, Source_2, Hole_2, Source_1, Hole_2).

% -----------------------------------------------------------------------------

% Predicates used by test that conform to same signature.

dl_append_expanded(Source_1,Hole_1,Source_2,Hole_2,Output) :-
    dl_append_expanded(Source_1,Hole_1,Source_2,Hole_2,Output,Output_hole),
    Output_hole = [].  % Convert open list to closed list

dl_append(Source_1,Hole_1,Source_2,Hole_2,Output) :-
    dl_append(Source_1,Hole_1,Source_2,Hole_2,Output,Output_hole),
    Output_hole = [].  % Convert open list to closed list

dl_append_edcg(Source_1,Hole_1,Source_2,Hole_2,Output) :-
    dl_append_edcg(Source_1,Hole_1,Source_2,Hole_2,Output,Output_hole),
    Output_hole = [].  % Convert open list to closed list

:- begin_tests(dl_append).

append_list_test_case_generator(        Hole_1 , Hole_1,        Hole_2 , Hole_2,            [] ).
append_list_test_case_generator(     [1|Hole_1], Hole_1,     [a|Hole_2], Hole_2,         [1,a] ).
append_list_test_case_generator(   [1,2|Hole_1], Hole_1,   [a,b|Hole_2], Hole_2,     [1,2,a,b] ).
append_list_test_case_generator( [1,2,3|Hole_1], Hole_1, [a,b,c|Hole_2], Hole_2, [1,2,3,a,b,c] ).
append_list_test_case_generator(     [1|Hole_1], Hole_1,        Hole_2 , Hole_2,           [1] ).
append_list_test_case_generator(        Hole_1 , Hole_1,     [a|Hole_2], Hole_2,           [a] ).

test(01,[forall(append_list_test_case_generator(Source_1,Hole_1,Source_2,Hole_2,Output))]) :-
    dl_append_expanded(Source_1,Hole_1,Source_2,Hole_2,Output).

test(02,[forall(append_list_test_case_generator(Source_1,Hole_1,Source_2,Hole_2,Output))]) :-
    dl_append(Source_1,Hole_1,Source_2,Hole_2,Output).

test(03,[forall(append_list_test_case_generator(Source_1,Hole_1,Source_2,Hole_2,Output))]) :-
    dl_append_edcg(Source_1,Hole_1,Source_2,Hole_2,Output).

:- end_tests(dl_append).