1 files changed, 75 insertions, 0 deletions
diff --git a/system/doc/extensions/list_comrehensions.erl b/system/doc/extensions/list_comrehensions.erl
new file mode 100644
index 0000000000..f6a23b5dca
--- /dev/null
+++ b/system/doc/extensions/list_comrehensions.erl
@@ -0,0 +1,75 @@
+-module(zf).
+
+-compile(export_all).
+
+
+%% Odd numbers.
+
+%%foo(L) -> [ X || X <- L, (X > X-1) == (X /= X-1) ].
+
+boo() -> [X||X <- [1,2,a,3,4,b,5,6], X > 3].
+boo1() -> [X||X <- [1,2,a,3,4,b,5,6], integer(X),X > 3].
+boo2() -> [{X,Y} || X <- [1,2,3], Y <- [a,b]].
+
+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.
+
+
+%% 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(A,B) ->
+    [ {X,Y} ||
+	X <- A,
+        Y <- B 
+    ].
+
+%% 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([]) -> [].
+
+%% append
+
+append(L)   ->  [X||L1<-L,X<-L1].
+
+map(Fun, L) -> [Fun(X)||X<-L].
+
+filter(Pred, L) -> [X||X<-L,Pred(X)].
+
+select(X, L) ->  [Y || {X1,Y} <- L, X == X1].