1 files changed, 118 insertions, 0 deletions
diff --git a/system/doc/extensions/list_comprehensions.erl b/system/doc/extensions/list_comprehensions.erl
new file mode 100644
index 0000000000..21ac562aa5
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+++ b/system/doc/extensions/list_comprehensions.erl
@@ -0,0 +1,118 @@
+-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).