%---------------------------------------------------------------------------%
% vim: ts=4 sw=4 et ft=mercury
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%
% The "maxlength" Benchmark
% Part of the DPPD Library.
% 
% A simple benchmark testing whether a partial deducer can perform tupling.
% The benchmark program traverses a list twice to get its length as well as
% the maximum value of the list. By tupling these traversals are merged into
% a single traversal. The benchmark program uses builtins but no negations.
% This particular benchmark program is treated in more detail in the
% technical report CW 225.

:- module maxlength.

:- interface.

:- pred maxlength is semidet.

:- implementation.

:- import_module list.
:- import_module max_length_impl.
:- import_module run.

maxlength :-
    max_length([1, 2, 3, 4, 3, 2, 1], Max1, Len1),
    use(Max1),
    use(Len1),
    max_length([], Max2, Len2),
    use(Max2),
    use(Len2),
    max_length([1, 5, 3, 2, 6, 3, 7, 3, 2, 1, 8, 5, 3, 5, 2, 3], Max3, Len3),
    use(Max3),
    use(Len3),
    max_length([1, 5, 3, 2, 6, 3, 7, 3, 2, 1, 8, 5, 3, 5, 2, 3], Max4, 5),
    use(Max4),
    max_length([1, 5, 3, 2, 6, 3, 7, 3, 2, 1, 8, 5, 3, 5, 2, 3], 3, Len5),
    use(Len5).

% The partial deduction query
% 
% :- max_length(L, Max, Len).
% 
% The run-time queries
% 
% :- max_length([1, 2, 3, 4, 3, 2, 1], Max, Len).
% :- max_length([], Max, Len).
% :- max_length([1, 5, 3, 2, 6, 3, 7, 3, 2, 1, 8, 5, 3, 5, 2, 3], Max, Len).
% :- max_length([1, 5, 3, 2, 6, 3, 7, 3, 2, 1, 8, 5, 3, 5, 2, 3], Max, 5).
% :- max_length([1, 5, 3, 2, 6, 3, 7, 3, 2, 1, 8, 5, 3, 5, 2, 3], 3, Len).
% 
% Example solution
% 
% With the ECCE partial deduction system one can obtain the following tupled
% program (which runs 20 % faster on Sicstus Prolog, but unfortunately
% 10% slower on Prolog by BIM - the problem is probably due to caching
% behaviour of the Sparc processor):
% 
% max_length__1(X1, X2, X3) :-
%     max1_conj__2(X1, 0, X2, X3).
% 
% max1_conj__2([], X1, X1, 0).
% max1_conj__2([X1 | X2], X3, X4, X5) :-
%     X1 =< X3,
%     max1_conj__2(X2, X3, X4, X6),
%     X5 is '+'(X6, 1).
% max1_conj__2([X1 | X2], X3, X4, X5) :-
%     X1 > X3,
%     max1_conj__2(X2, X1, X4, X6),
%     X5 is '+'(X6, 1).
% 
% Michael Leuschel / K.U. Leuven / michael@cs.kuleuven.ac.be