San an kou

src/riichi.erl

@@ -10,6 +10,7 @@
 
 -export([
          is_valid_tile/1,
+         is_open/1,
          dora/1,
          nearest/2,
          score/3,
@@ -32,6 +33,17 @@ is_valid_tile(#tile{suit=Suit, value=Value}) ->
 is_valid_tile(_) ->
     false.
 
+-spec is_open(hand() | meld() | tile()) -> boolean().
+is_open(#tile{from=draw}) ->
+    false;
+is_open(#tile{}) ->
+    true;
+is_open(#meld{tiles=Tiles}) ->
+    lists:any(fun is_open/1, Tiles);
+is_open(#hand{tiles=Tiles, melds=Melds}) ->
+    lists:any(fun is_open/1, Tiles)
+        orelse lists:any(fun is_open/1, Melds).
+
 -spec dora(tile()) -> tile().
 dora(#tile{suit=dragon, value=Value}=Indicator) ->
     case Value of

src/yaku.erl

@@ -19,6 +19,7 @@
          san_shoku_douko/2,
          san_kan_tsu/2,
          toi_toi/2,
+         san_an_kou/2,
          kokushi_musou/2,
          ryuu_iisou/2,
          dai_san_gen/2]).
@@ -155,6 +156,14 @@ toi_toi(#game{}, #player{hand=#hand{melds=Melds}}) ->
                   lists:member(T, [pon,kan])],
     length(Pons) =:= 4.
 
+%% @doc Returns true for a San an kou hand
+%%      Hand must contain three concealed triplets
+san_an_kou(#game{}, #player{hand=#hand{melds=Melds}}) ->
+    ClosedPons = [M || M = #meld{type=T} <- Melds,
+                       not riichi:is_open(M),
+                       lists:member(T, [pon,kan])],
+    length(ClosedPons) =:= 3.
+
 %% @doc Returns true for a 7-pair hand.
 -spec chiitoitsu(game(), player()) -> boolean().
 chiitoitsu(#game{}, #player{hand=#hand{tiles=[], melds=Melds}})

test/riichi_yaku_tests.erl

@@ -92,6 +92,13 @@ toi_toi_test() ->
                         #meld{type=pon, tiles=[#tile{suit=pin, value=V} || V <- [8,8,8]]}]},
     ?assertEqual(true, yaku:toi_toi(#game{}, #player{hand=Hand, drawn={tsumo, #tile{suit=dragon, value=red}}})).
     
+san_an_kou_test() ->
+    Hand = #hand{melds=[#meld{type=pair, tiles=lists:duplicate(2, #tile{suit=sou, value=8})},
+                        #meld{type=kan, tiles=[#tile{suit=sou, value=V} || V <- [1,1,1,1]]},
+                        #meld{type=kan, tiles=[#tile{suit=man, value=V} || V <- [1,1,1,1]]},
+                        #meld{type=pon, tiles=[#tile{suit=pin, value=V} || V <- [1,1,1]]},
+                        #meld{type=chii, tiles=[#tile{suit=man, value=V} || V <- [6,7,8]]}]},
+    ?assertEqual(true, yaku:san_an_kou(#game{}, #player{hand=Hand, drawn={tsumo, #tile{suit=dragon, value=red}}})).
 
 chiitoitsu_test() ->
     Hand = #hand{melds=[#meld{type=pair, tiles=lists:duplicate(2, #tile{suit=pin, value=V})} || V <- lists:seq(1,7)]},