Merge 74cdcdd into b16b3e1

README.md

@@ -71,3 +71,26 @@ With zlist you are working with potentially infinite data.
 Don't use ```to_list/1```, ```foreach/2```, ```fold/3``` functions
 until you know that zlist is finite state.
 Use ```dropwhen/1``` before, or ```take/2``` instead.
+
+### QLC ###
+
+Zlists supports alternative syntax with QLC query language, example:
+
+```
+> Zs = zlist:seq(1, 20),
+> Q1 = qlc:q([{C,B,A} || A <- zlist:table(Zs), B <- zlist:table(Zs), C <- zlist:table(Zs),
+                       A =< B, A*A + B*B == C*C]),
+> Q2 = qlc:sort(Q1, [{order, descending}]),
+> Cursor = qlc:cursor(Q2).
+> qlc:next_answers(Cursor, 2).
+> [{20,16,12},{17,15,8}]
+>
+> qlc:next_answers(Cursor, 5). %only 4 available
+> [{15,12,9}, {13,12,5},{10,8,6},{5,4,3}]
+>
+> qlc:next_answers(Cursor, 1). %no answers available
+> []
+```
+
+Use this with care, because it's may make your lazy lists strict.
+For another QLC functionality, like cache, sorting, joining etc see http://erlang.org/doc/man/qlc.html

src/zlist.erl

@@ -24,7 +24,9 @@
          take_by/2,
 
          from_list/1,
-         to_list/1
+         to_list/1,
+
+         table/1
         ]).
 
 -type zlist(A) :: fun(() -> maybe_improper_list(A, zlist(A))) | empty_zlist().
@@ -248,3 +250,6 @@ take_by(N, Zlist) when N > 0 ->
             {List, RestZ} -> [List] ++ take_by(N, RestZ)
         end
     end.
+
+table(Zs) ->
+    qlc:table(Zs, []).

test/zlist_tests.erl

@@ -209,3 +209,15 @@ take_by_test() ->
     GroupedZ = zlist:take_by(100, ZSeq),
     [_|RestZ] = GroupedZ(),
     ?assertEqual([], RestZ()).
+
+-include_lib("stdlib/include/qlc.hrl").
+qlc_test() ->
+    Zs = zlist:seq(1, 20),
+    Q1 = qlc:q([{C,B,A} || A <- zlist:table(Zs), B <- zlist:table(Zs), C <- zlist:table(Zs),
+                           A =< B, A*A + B*B == C*C]),
+    Q2 = qlc:sort(Q1, [{order, descending}]),
+    Cursor = qlc:cursor(Q2),
+    ?assertEqual([{20,16,12},{17,15,8}], qlc:next_answers(Cursor, 2)),
+    ?assertEqual([{15,12,9}, {13,12,5},{10,8,6},{5,4,3}], qlc:next_answers(Cursor, 5)), %only 4 available
+    ?assertEqual([], qlc:next_answers(Cursor, 1)), %no answers
+    ok = qlc:delete_cursor(Cursor).