1 files changed, 150 insertions, 0 deletions
diff --git a/gen/result.erl b/gen/result.erl
new file mode 100644
index 0000000..d3337e2
--- /dev/null
+++ b/gen/result.erl
@@ -0,0 +1,150 @@
+-module(result).
+-include_lib("eunit/include/eunit.hrl").
+
+-export([is_ok/1, is_error/1, map/2, map_error/2, flatten/1, flat_map/2, unwrap/2]).
+
+is_ok(Result) ->
+    case Result of
+        {error, _} ->
+            false;
+
+        {ok, _} ->
+            true
+    end.
+
+-ifdef(TEST).
+is_ok_test() ->
+    _ = expect:true(is_ok({ok, 1})),
+    expect:false(is_ok({error, 1})).
+-endif.
+
+is_error(Result) ->
+    case Result of
+        {ok, _} ->
+            false;
+
+        {error, _} ->
+            true
+    end.
+
+-ifdef(TEST).
+is_error_test() ->
+    _ = expect:false(is_error({ok, 1})),
+    expect:true(is_error({error, 1})).
+-endif.
+
+map(Result, Fun) ->
+    case Result of
+        {ok, X} ->
+            {ok, Fun(X)};
+
+        {error, _} ->
+            Result
+    end.
+
+-ifdef(TEST).
+map_test() ->
+    _ = fun(Capture1) ->
+        expect:equal(Capture1, {ok, 2})
+    end(fun(Capture1) -> map(Capture1, fun(X) -> X + 1 end) end({ok, 1})),
+    fun(Capture1) ->
+        expect:equal(Capture1, {error, 1})
+    end(fun(Capture1) -> map(Capture1, fun(X) -> X + 1 end) end({error, 1})).
+-endif.
+
+map_error(Result, Fun) ->
+    case Result of
+        {ok, _} ->
+            Result;
+
+        {error, Error} ->
+            {error, Fun(Error)}
+    end.
+
+-ifdef(TEST).
+map_error_test() ->
+    _ = fun(Capture1) ->
+        expect:equal(Capture1, {ok, 1})
+    end(fun(Capture1) -> map_error(Capture1, fun(X) -> X + 1 end) end({ok, 1})),
+    fun(Capture1) ->
+        expect:equal(Capture1, {error, 2})
+    end(fun(Capture1) ->
+            map_error(Capture1, fun(X) -> X + 1 end)
+        end({error, 1})).
+-endif.
+
+flatten(Result) ->
+    case Result of
+        {ok, X} ->
+            X;
+
+        {error, Error} ->
+            {error, Error}
+    end.
+
+-ifdef(TEST).
+flatten_test() ->
+    _ = fun(Capture1) ->
+        expect:equal(Capture1, {ok, 1})
+    end(flatten({ok, {ok, 1}})),
+    _ = fun(Capture1) ->
+        expect:equal(Capture1, {error, 1})
+    end(flatten({ok, {error, 1}})),
+    _ = fun(Capture1) ->
+        expect:equal(Capture1, {error, 1})
+    end(flatten({error, 1})),
+    fun(Capture1) ->
+        expect:equal(Capture1, {error, {error, 1}})
+    end(flatten({error, {error, 1}})).
+-endif.
+
+flat_map(Result, Fun) ->
+    case Result of
+        {ok, X} ->
+            case Fun(X) of
+                {ok, Y} ->
+                    {ok, Y};
+
+                {error, Y1} ->
+                    {error, Y1}
+            end;
+
+        {error, _} ->
+            Result
+    end.
+
+-ifdef(TEST).
+flat_map_test() ->
+    _ = fun(Capture1) ->
+        expect:equal(Capture1, {error, 1})
+    end(fun(Capture1) ->
+            flat_map(Capture1, fun(X) -> {ok, X + 1} end)
+        end({error, 1})),
+    _ = fun(Capture1) ->
+        expect:equal(Capture1, {ok, 2})
+    end(fun(Capture1) ->
+            flat_map(Capture1, fun(X) -> {ok, X + 1} end)
+        end({ok, 1})),
+    fun(Capture1) ->
+        expect:equal(Capture1, {error, 1})
+    end(fun(Capture1) ->
+            flat_map(Capture1, fun(Unused) -> {error, 1} end)
+        end({ok, 1})).
+-endif.
+
+unwrap(Result, Default) ->
+    case Result of
+        {ok, V} ->
+            V;
+
+        {error, _} ->
+            Default
+    end.
+
+-ifdef(TEST).
+unwrap_test() ->
+    _ = fun(Capture1) -> expect:equal(Capture1, 1) end(unwrap({ok, 1}, 50)),
+    fun(Capture1) ->
+        expect:equal(Capture1, 50)
+    end(unwrap({error, <<"nope">>}, 50)).
+-endif.