1 files changed, 45 insertions, 0 deletions
diff --git a/learn-you-some-erlang/zoo.erl b/learn-you-some-erlang/zoo.erl
new file mode 100644
index 0000000..1e3c2eb
--- /dev/null
+++ b/learn-you-some-erlang/zoo.erl
@@ -0,0 +1,45 @@
+-module(zoo).
+-export([main/0]).
+
+-type red_panda() :: bamboo | birds | eggs | berries.
+-type squid() :: sperm_whale.
+-type food(A) :: fun(() -> A).
+
+-spec feeder(red_panda) -> food(red_panda());
+            (squid) -> food(squid()).
+feeder(red_panda) ->
+    fun() ->
+        element(random:uniform(4), {bamboo, birds, eggs, berries})
+    end;
+feeder(squid) ->
+    fun() -> sperm_whale end.
+
+-spec feed_red_panda(food(red_panda())) -> red_panda().
+feed_red_panda(Generator) ->
+    Food = Generator(),
+    io:format("feeding ~p to the red panda~n", [Food]),
+    Food.
+
+-spec feed_squid(food(squid())) -> squid().
+feed_squid(Generator) ->
+    Food = Generator(),
+    io:format("feeding ~p to the squid~n", [Food]),
+    Food.
+
+main() ->
+    %% Random seeding
+    <<A:32, B:32, C:32>> = crypto:rand_bytes(12),
+    random:seed(A, B, C),
+    %% The zoo buys a feeder for both the red panda and squid
+    FeederRP = feeder(red_panda),
+    FeederSquid = feeder(squid),
+    %% Time to feed them! If we do it correctly at least once,
+    %% Then no warning ever happens. Comment the two lines
+    %% below to enable dialyzer figuring stuff out! This is likely
+    %% failing because Dialyzer sees both calls as valid and thus
+    %% needs not to reevaluate them again.
+    %feed_squid(FeederSquid),
+    %feed_red_panda(FeederRP),
+    %% This should not be right!
+    feed_squid(FeederRP),
+    feed_red_panda(FeederSquid).