feat: Extend do_either API

README.md

@@ -11,7 +11,7 @@ implementations for commonly used class instances.
 To install the latest version of `do` from [`hex`](https://hex.pm/packages/do),
 add `do` to the `deps` in your rebar config file:
 
-    {do, "1.8.1"}
+    {do, "1.9.0"}
 
 ### What's in the box
 

doc/do_either.html

@@ -48,11 +48,19 @@ <h3 class="typedecl"><a name="type-traversable">traversable()</a></h3>
 <h2><a name="index">Function Index</a></h2>
 <table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#bind-2">bind/2</a></td><td></td></tr>
 <tr><td valign="top"><a href="#do-2">do/2</a></td><td></td></tr>
+<tr><td valign="top"><a href="#either-3">either/3</a></td><td></td></tr>
+<tr><td valign="top"><a href="#errors-1">errors/1</a></td><td></td></tr>
 <tr><td valign="top"><a href="#fmap-2">fmap/2</a></td><td></td></tr>
+<tr><td valign="top"><a href="#from_error-2">from_error/2</a></td><td></td></tr>
+<tr><td valign="top"><a href="#from_ok-2">from_ok/2</a></td><td></td></tr>
+<tr><td valign="top"><a href="#is_error-1">is_error/1</a></td><td></td></tr>
+<tr><td valign="top"><a href="#is_ok-1">is_ok/1</a></td><td></td></tr>
 <tr><td valign="top"><a href="#lift-1">lift/1</a></td><td></td></tr>
 <tr><td valign="top"><a href="#liftA2-2">liftA2/2</a></td><td></td></tr>
 <tr><td valign="top"><a href="#liftm-2">liftm/2</a></td><td></td></tr>
 <tr><td valign="top"><a href="#liftmz-2">liftmz/2</a></td><td></td></tr>
+<tr><td valign="top"><a href="#oks-1">oks/1</a></td><td></td></tr>
+<tr><td valign="top"><a href="#partition-1">partition/1</a></td><td></td></tr>
 <tr><td valign="top"><a href="#pure-1">pure/1</a></td><td></td></tr>
 <tr><td valign="top"><a href="#sequence-1">sequence/1</a></td><td></td></tr>
 <tr><td valign="top"><a href="#then-2">then/2</a></td><td></td></tr>
@@ -72,9 +80,45 @@ <h3 class="function"><a name="do-2">do/2</a></h3>
 <p> </p>
 </div>
 
+<h3 class="function"><a name="either-3">either/3</a></h3>
+<div class="spec">
+<p><tt>either(F1::<a href="#type-fn">fn</a>(A, C), F2::<a href="#type-fn">fn</a>(B, C), Either::<a href="#type-either">either</a>(A, B)) -&gt; C</tt><br></p>
+<p> </p>
+</div>
+
+<h3 class="function"><a name="errors-1">errors/1</a></h3>
+<div class="spec">
+<p><tt>errors(Eithers::[<a href="#type-either">either</a>(A, term())]) -&gt; [A]</tt><br></p>
+<p> </p>
+</div>
+
 <h3 class="function"><a name="fmap-2">fmap/2</a></h3>
 <div class="spec">
-<p><tt>fmap(F::<a href="#type-fn">fn</a>(B, C), X2::<a href="#type-either">either</a>(A, B)) -&gt; <a href="#type-either">either</a>(A, C)</tt><br></p>
+<p><tt>fmap(F::<a href="#type-fn">fn</a>(B, C), Either::<a href="#type-either">either</a>(A, B)) -&gt; <a href="#type-either">either</a>(A, C)</tt><br></p>
+<p> </p>
+</div>
+
+<h3 class="function"><a name="from_error-2">from_error/2</a></h3>
+<div class="spec">
+<p><tt>from_error(A, Either::<a href="#type-either">either</a>(A, term())) -&gt; A</tt><br></p>
+<p> </p>
+</div>
+
+<h3 class="function"><a name="from_ok-2">from_ok/2</a></h3>
+<div class="spec">
+<p><tt>from_ok(B, Either::<a href="#type-either">either</a>(term(), B)) -&gt; B</tt><br></p>
+<p> </p>
+</div>
+
+<h3 class="function"><a name="is_error-1">is_error/1</a></h3>
+<div class="spec">
+<p><tt>is_error(Either::<a href="#type-either">either</a>(term(), term())) -&gt; boolean()</tt><br></p>
+<p> </p>
+</div>
+
+<h3 class="function"><a name="is_ok-1">is_ok/1</a></h3>
+<div class="spec">
+<p><tt>is_ok(Either::<a href="#type-either">either</a>(term(), term())) -&gt; boolean()</tt><br></p>
 <p> </p>
 </div>
 
@@ -86,7 +130,7 @@ <h3 class="function"><a name="lift-1">lift/1</a></h3>
 
 <h3 class="function"><a name="liftA2-2">liftA2/2</a></h3>
 <div class="spec">
-<p><tt>liftA2(X1::<a href="#type-either">either</a>(A1, <a href="#type-fn">fn</a>(B, C)), Either::<a href="#type-either">either</a>(A2, B)) -&gt; <a href="#type-either">either</a>(A1 | A2, C)</tt><br></p>
+<p><tt>liftA2(Either::<a href="#type-either">either</a>(A1, <a href="#type-fn">fn</a>(B, C)), Either::<a href="#type-either">either</a>(A2, B)) -&gt; <a href="#type-either">either</a>(A1 | A2, C)</tt><br></p>
 <p> </p>
 </div>
 
@@ -102,6 +146,18 @@ <h3 class="function"><a name="liftmz-2">liftmz/2</a></h3>
 <p> </p>
 </div>
 
+<h3 class="function"><a name="oks-1">oks/1</a></h3>
+<div class="spec">
+<p><tt>oks(Eithers::[<a href="#type-either">either</a>(term(), B)]) -&gt; [B]</tt><br></p>
+<p> </p>
+</div>
+
+<h3 class="function"><a name="partition-1">partition/1</a></h3>
+<div class="spec">
+<p><tt>partition(Eithers::[<a href="#type-either">either</a>(A, B)]) -&gt; {[A], [B]}</tt><br></p>
+<p> </p>
+</div>
+
 <h3 class="function"><a name="pure-1">pure/1</a></h3>
 <div class="spec">
 <p><tt>pure(B) -&gt; <a href="#type-either">either</a>(term(), B)</tt><br></p>

src/do.app.src

@@ -1,6 +1,6 @@
 {application, do,
  [{description, "Monads, Functors and Do-Notation for Erlang"},
-  {vsn, "1.8.1"},
+  {vsn, "1.9.0"},
   {registered, []},
   {applications,
    [kernel,

src/do_either.erl

@@ -11,16 +11,29 @@
 -behaviour(do_monad).
 
 %%%_* Exports =================================================================
--define(API, [ bind/2,
-               do/2,
+-define(API, [ % functor
                fmap/2,
-               lift/1,
+               % applicative
                liftA2/2,
-               liftm/2,
-               liftmz/2,
                pure/1,
                sequence/1,
-               then/2]).
+               % monad
+               bind/2,
+               do/2,
+               lift/1,
+               liftm/2,
+               then/2,
+               % either
+               liftmz/2,
+               either/3,
+               errors/1,
+               oks/1,
+               is_error/1,
+               is_ok/1,
+               from_error/2,
+               from_ok/2,
+               partition/1]).
+
 -export(?API).
 -ignore_xref(?API).
 
@@ -31,12 +44,12 @@
 
 %%%_* Code ====================================================================
 %%%_* functor -----------------------------------------------------------------
--spec fmap(fn(B, C), either(A, B)) -> either(A, C).
+-spec fmap(fn(B, C), Either :: either(A, B)) -> either(A, C).
 fmap(F, {error, A}) when ?isF1(F) -> {error, A};
 fmap(F, {ok, B})    when ?isF1(F) -> {ok, F(B)}. 
 
 %%%_* applicative -------------------------------------------------------------
--spec liftA2(either(A1, fn(B, C)), either(A2, B)) -> either(A1 | A2, C).
+-spec liftA2(Either :: either(A1, fn(B, C)), either(A2, B)) -> either(A1 | A2, C).
 liftA2({ok, F}, Either) when ?isF1(F) -> fmap(F, Either);
 liftA2({error, Reason}, _)            -> {error, Reason}.
 
@@ -59,11 +72,48 @@ lift(F) -> do_monad:lift(F, ?MODULE).
 -spec liftm(fun(), [either(_, B)]) -> either(_, B).
 liftm(F, Eithers) -> do_monad:liftm(F, Eithers, ?MODULE).
 
+-spec then(either(A, _), fn(either(B, C))) -> either(A | B, C).
+then(Either, F) -> do_monad:then(Either, F, ?MODULE).
+
+%%%_* either ------------------------------------------------------------------
 -spec liftmz(fun(), [fn(either(_, B))]) -> either(_, B).
 liftmz(F, Eithers) -> do_monad:liftmz(F, Eithers, ?MODULE).
 
--spec then(either(A, _), fn(either(B, C))) -> either(A | B, C).
-then(Either, F) -> do_monad:then(Either, F, ?MODULE).
+-spec either(fn(A, C), fn(B, C), Either :: either(A, B)) -> C.
+either(F1, F2, {error, A}) when ?isF1(F1), ?isF1(F2) -> F1(A);
+either(F1, F2, {ok, B})    when ?isF1(F1), ?isF1(F2) -> F2(B).
+
+-spec errors([either(A, _)]) -> [A].
+errors(Eithers) when is_list(Eithers) ->
+  lists:filtermap(fun({error, A}) -> {true, A};
+                     ({ok, _B})   -> false end, Eithers).
+
+-spec oks([either(_, B)]) -> [B].
+oks(Eithers) when is_list(Eithers) ->
+  lists:filtermap(fun({ok, B})     -> {true, B};
+                     ({error, _A}) -> false end, Eithers).
+
+
+-spec is_error(Either :: either(_, _)) -> boolean().
+is_error({error, _}) -> true;
+is_error({ok, _})    -> false.
+
+-spec is_ok(either(_, _)) -> boolean().
+is_ok(Either) -> not is_error(Either).
+
+-spec from_error(A, Either :: either(A, _)) -> A.
+from_error(_A, {error, A}) -> A;
+from_error(A, {ok, _B})    -> A.
+
+-spec from_ok(B, Either :: either(_, B)) -> B.
+from_ok(_B, {ok, B})    -> B;
+from_ok(B, {error, _A}) -> B.
+
+-spec partition([either(A, B)]) -> {[A], [B]}.
+partition(Eithers) when is_list(Eithers) ->
+  lists:foldr(fun({error, A}, {As, Bs}) -> {[A | As], Bs};
+                 ({ok, B},    {As, Bs}) -> {As, [B | Bs]} end,
+              {[], []}, Eithers).
 
 %%%_* internal ----------------------------------------------------------------
 flat({ok, {error, A}}) -> {error, A};
@@ -120,4 +170,38 @@ sequence_test() ->
   ?assertEqual({ok, #{a => 1, b => 2}}, sequence(#{a => {ok, 1}, b => {ok, 2}})),
   ?assertEqual({error, reason},         sequence(#{a => {ok, 1}, b => {error, reason}})).
 
+either_test() ->
+  F1 = fun(X) -> X end,
+  F2 = fun(_) -> 0 end,
+  ?assertEqual(1, either(F2, F1, {ok, 1})),
+  ?assertEqual(2, either(F1, F2, {error, 2})).
+
+errors_test() ->
+  ?assertEqual([],     errors([])),
+  ?assertEqual([1, 2], errors([{ok, 3}, {error, 1}, {error, 2}, {ok, 4}])).
+
+oks_test() ->
+  ?assertEqual([],     oks([])),
+  ?assertEqual([3, 4], oks([{ok, 3}, {error, 1}, {error, 2}, {ok, 4}])).
+
+is_error_test() ->
+  ?assertEqual(true,  is_error({error, 1})),
+  ?assertEqual(false, is_error({ok, 1})).
+
+is_ok_test() ->
+  ?assertEqual(false, is_ok({error, 1})),
+  ?assertEqual(true,  is_ok({ok, 1})).
+
+from_error_test() ->
+  ?assertEqual(1, from_error(2, {error, 1})),
+  ?assertEqual(2, from_error(2, {ok, 1})).
+
+from_ok_test() ->
+  ?assertEqual(1, from_ok(2, {ok, 1})),
+  ?assertEqual(2, from_ok(2, {error, 1})).
+
+partition_test() ->
+  ?assertEqual({[], []},         partition([])),
+  ?assertEqual({[1, 2], [3, 4]}, partition([{ok, 3}, {error, 1}, {error, 2}, {ok, 4}])).
+
 -endif.

src/do_maybe.erl

@@ -73,13 +73,13 @@ lift(F) -> do_monad:lift(F, ?MODULE).
 -spec liftm(fun(), [maybe(A)]) -> maybe(A).
 liftm(F, Maybes) -> do_monad:liftm(F, Maybes, ?MODULE).
 
--spec liftmz(fun(), [fn(maybe(A))]) -> maybe(A).
-liftmz(F, Maybes) -> do_monad:liftmz(F, Maybes, ?MODULE).
-
 -spec then(maybe(_), fn(maybe(A))) -> maybe(A).
 then(Maybe, F) -> do_monad:then(Maybe, F, ?MODULE).
 
 %%%_* maybe -------------------------------------------------------------------
+-spec liftmz(fun(), [fn(maybe(A))]) -> maybe(A).
+liftmz(F, Maybes) -> do_monad:liftmz(F, Maybes, ?MODULE).
+
 -spec maybe(B, fn(A, B), Maybe :: maybe(A)) -> B.
 maybe(B, F, nothing)   when ?isF1(F) -> B;
 maybe(_, F, {just, A}) when ?isF1(F) -> F(A).