hg.stevelosh.com > temperance

test/99.pl @ ba205f6b2875 

Excise the stupid fucking `set-*` opcodes

The book uses the horribly-confusingly-named `set-*` operations for handling
subterms in query mode.  The author does this because he claims this is both
easier to understand and more performant.  In reality it is neither of these
things.

If you just name the subterm-handling opcodes something not completely stupid,
like `handle-subterm-*` instead of `unify-*` it becomes obvious what they do.

Also, despite the fact that `put-*` instructions now need to set the WAM's
`mode`, we still get about a 10% speedup here, likely from some combination of
reducing the VM loop code size and simplifying the compilation process.  So it's
not even more performant.

TL;DR: Just say "No" to `set-*`.
author Steve Losh <steve@stevelosh.com>
date Sun, 10 Jul 2016 14:21:18 +0000
parents 5e0cca5174a8
children 4abb7eda96cb 
% 99 Prolog Problems
% from http://www.ic.unicamp.br/~meidanis/courses/mc336/2009s2/prolog/problemas/
%
% Solutions to at least a few of these, for testing purposes.

% P01
my_last(X, [X]).
my_last(X, [_ | T]) :-
    my_last(X, T).

% P02
my_lastbutone(X, [X, _]).
my_lastbutone(X, [_ | T]) :-
    my_lastbutone(X, T).

% P03
my_nth(X, [X | _], 1).
my_nth(X, [_ | T], N) :-
    M is N - 1,
    my_nth(X, T, M).

% P04
my_len([], 0).
my_len([_ | T], Length) :-
    my_len(T, M),
    Length is M + 1.

my_len_acc([], A, A).
my_len_acc([_ | T], A, Length) :-
    B is A + 1,
    my_len_acc(T, B, Length).

my_len2(L, Length) :-
    my_len_acc(L, 0, Length).

% P05
my_reverse_acc([], Acc, Acc).
my_reverse_acc([X | T], Acc, Reversed) :-
    my_reverse_acc(T, [X | Acc], Reversed).

my_reverse(L, R) :-
    my_reverse_acc(L, [], R).

% P06
my_palindrome(L) :-
    my_reverse(L, L).

% P07
my_flatten([], []).

my_flatten([Atom | Tail], [Atom | FlatTail]) :-
    \+ is_list(Atom),
    my_flatten(Tail, FlatTail).

my_flatten([HeadList | Tail], Flattened) :-
    is_list(HeadList),
    my_flatten(HeadList, FlatHeadList),
    my_flatten(Tail, FlatTail),
    append(FlatHeadList, FlatTail, Flattened).

% P08
my_compress_acc([], A, A).

my_compress_acc([X | T], [X | Acc], Compressed) :-
    my_compress_acc(T, [X | Acc], Compressed).

my_compress_acc([X | T], [Y | Acc], Compressed) :-
    X \= Y,
    my_compress_acc(T, [X, Y | Acc], Compressed).

my_compress([H | T], Compressed) :-
    my_compress_acc(T, [H], ReverseCompressed),
    my_reverse(ReverseCompressed, Compressed).

their_compress([],[]).
their_compress([X],[X]).
their_compress([X,X|Xs],Zs) :- compress([X|Xs],Zs).
their_compress([X,Y|Ys],[X|Zs]) :- X \= Y, compress([Y|Ys],Zs).

% P09
my_pack([], []).
my_pack([X], [[X]]).

my_pack([X | Tail], [[X] | ResultTail]) :-
    my_pack(Tail, ResultTail),
    ResultTail = [[Y | _] | _],
    X \= Y.

my_pack([X | Tail], [[X, X | XS] | ResultTail]) :-
    my_pack(Tail, [[X | XS] | ResultTail]).

their_pack([],[]).
their_pack([X | Tail], [Chunk | PackedTail]) :-
    their_transfer(X, [X | Tail], Remaining, Chunk),
    their_pack(Remaining, PackedTail).

% transfer(X,Xs,Ys,Z) Ys is the list that remains from the list Xs
%    when all leading copies of X are removed and transfered to Z

their_transfer(_, [], [], []).

their_transfer(X, [Y | Ys], [Y | Ys], []) :-
    X \= Y.

their_transfer(X, [X | Xs], Ys, [X | Zs]) :-
    their_transfer(X, Xs, Ys, Zs).