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authorErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
committerErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
commit84adefa331c4159d432d22840663c38f155cd4c1 (patch)
treebff9a9c66adda4df2106dfd0e5c053ab182a12bd /system/doc/extensions/list_comprehensions.erl
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The R13B03 release.OTP_R13B03
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+-module(t).
+-author('[email protected]').
+
+%%-export([test/2]).
+-compile(export_all).
+
+%% Odd numbers.
+
+%%foo(L) -> [ X || X <- L, (X > X-1) == (X /= X-1) ].
+
+bar(L) -> [ X || X <- L, integer(X), gt(X, 3) ].
+
+bar(L, M) -> [ Y || X <- L, integer(X), gt(X, 3),
+ Y <- M, float(Y), gt(X, Y)
+ ].
+
+baz(L) -> [ X || X <- L, atom(X) ].
+
+buz(L, Min) -> [ X || Min > 3, X <- L, X >= Min ].
+
+gt(X, Y) when X > Y -> true;
+gt(X, Y) -> false.
+
+%% Turn a list into a set.
+make_set([]) -> [];
+make_set([H|T]) ->
+ [H|[
+ Y || Y <- make_set(T),
+ Y =/= H
+ ]].
+
+%% Return the Pythagorean triangles with sides
+%% of total length less than N
+pyth(N) ->
+ [ {A,B,C} ||
+ A <- lists:seq(1,N),
+ B <- lists:seq(1,N),
+ C <- lists:seq(1,N),
+ A+B+C =< N,
+ A*A+B*B == C*C
+ ].
+
+%% Cut the search space a bit..
+pyth2(N) ->
+ [ {A,B,C} ||
+ A <- lists:seq(1,N),
+ B <- lists:seq(1,N-A+1),
+ C <- lists:seq(1,N-A-B+2),
+ A+B+C =< N,
+ A*A+B*B == C*C ].
+
+%% Return the Cartesian product
+cp() ->
+ [ {X,Y} ||
+ X <- a(),
+ Y <- b()
+ ].
+
+cp(A,B) when list(A),list(B) ->
+ [ {X,Y} ||
+ X <- A,
+ Y <- B
+ ].
+
+%a() -> 1/0.
+a() -> [a,b].
+b() -> [1,2,3].
+
+%% Return all permutations of a list
+perms([]) -> [[]];
+perms(L) -> [ [H|T] || H <- L, T <- perms(L--[H]) ].
+
+%% Quick sort
+sort([X|Xs]) ->
+ sort([ Y || Y <- Xs, Y < X ]) ++
+ [X] ++
+ sort([ Y || Y <- Xs, Y >= X ]);
+sort([]) -> [].
+
+%% Vector addition
+vecAdd(Xs,Ys) ->
+ [ X+Y || {X,Y} <- zip(Xs,Ys) ].
+
+zip([X|Xs],[Y|Ys]) -> [{X,Y}|zip(Xs,Ys)];
+zip([],[]) -> [].
+
+qsort([X|Xs]) ->
+ qsort(lt(X,Xs))
+ ++ [X] ++
+ qsort(ge(X,Xs));
+qsort([]) -> [].
+
+lt(X,[H|T]) when X>H -> [H|lt(X,T)];
+lt(X,[_|T]) -> lt(X,T);
+lt(_,[]) -> [].
+
+ge(X,[H|T]) when X=<H -> [H|ge(X,T)];
+ge(X,[_|T]) -> ge(X,T);
+ge(_,[]) -> [].
+
+test(1,N) -> statistics(runtime),test1(N),statistics(runtime);
+test(2,N) -> statistics(runtime),test2(N),statistics(runtime);
+test(3,N) -> statistics(runtime),test3(N),statistics(runtime).
+
+test1(0) -> true;
+test1(N) ->
+ sort([21,12,45,1,3,87,55,77,11,20,6,99,91,13,14,15,66,62,69,71,67,82,83,84,87,86,85]),
+ test1(N-1).
+
+test2(0) -> true;
+test2(N) ->
+ qsort([21,12,45,1,3,87,55,77,11,20,6,99,91,13,14,15,66,62,69,71,67,82,83,84,87,86,85]),
+ test2(N-1).
+
+test3(0) -> true;
+test3(N) ->
+ lists:sort([21,12,45,1,3,87,55,77,11,20,6,99,91,13,14,15,66,62,69,71,67,82,83,84,87,86,85]),
+ test3(N-1).