1 files changed, 43 insertions, 0 deletions
diff --git a/learn-you-some-erlang/tree.erl b/learn-you-some-erlang/tree.erl
new file mode 100644
index 0000000..3cda7c3
--- /dev/null
+++ b/learn-you-some-erlang/tree.erl
@@ -0,0 +1,43 @@
+-module(tree).
+-export([empty/0, insert/3, lookup/2, has_value/2]).
+
+empty() -> {node, 'nil'}.
+
+insert(Key, Val, {node, 'nil'}) ->
+    {node, {Key, Val, {node, 'nil'}, {node, 'nil'}}};
+insert(NewKey, NewVal, {node, {Key, Val, Smaller, Larger}}) when NewKey < Key ->
+    {node, {Key, Val, insert(NewKey, NewVal, Smaller), Larger}};
+insert(NewKey, NewVal, {node, {Key, Val, Smaller, Larger}}) when NewKey > Key ->
+    {node, {Key, Val, Smaller, insert(NewKey, NewVal, Larger)}};
+insert(Key, Val, {node, {Key, _, Smaller, Larger}}) ->
+    {node, {Key, Val, Smaller, Larger}}.
+
+lookup(_, {node, 'nil'}) ->
+    undefined;
+lookup(Key, {node, {Key, Val, _, _}}) ->
+    {ok, Val};
+lookup(Key, {node, {NodeKey, _, Smaller, _}}) when Key < NodeKey ->
+    lookup(Key, Smaller);
+lookup(Key, {node, {_, _, _, Larger}}) ->
+    lookup(Key, Larger).
+
+%%---------------------------------------------------------
+%% The code after this comment is added in the errors and
+%% exceptions chapter. Ignore it if you're still reading
+%% the chapter about recursion.
+%%---------------------------------------------------------
+
+has_value(Val, Tree) -> 
+    try has_value1(Val, Tree) of
+        _ -> false
+    catch
+        true -> true
+    end.
+
+has_value1(_, {node, 'nil'}) ->
+    false;
+has_value1(Val, {node, {_, Val, _, _}}) ->
+    throw(true);
+has_value1(Val, {node, {_, _, Left, Right}}) ->
+    has_value1(Val, Left),
+    has_value1(Val, Right).