Implement hope_result:(map_error and tag_error)

[hope.git] / src / hope_result.erl

diff --git a/src/hope_result.erl b/src/hope_result.erl
index 7cae0a3..dec6e79 100644 (file)
--- a/src/hope_result.erl
+++ b/src/hope_result.erl
@@ -9,6 +9,8 @@
 -export(
     [ return/1
     , map/2
+    , map_error/2
+    , tag_error/2
     , pipe/2
     , lift_exn/1
     , lift_exn/2
@@ -33,6 +35,20 @@ map({ok, X}, F) ->
 map({error, _}=Error, _) ->
     Error.
 
+-spec map_error(t(A, B), fun((B) -> (C))) ->
+    t(A, C).
+map_error({ok, _}=Ok, _) ->
+    Ok;
+map_error({error, Reason}, F) ->
+    {error, F(Reason)}.
+
+-spec tag_error(t(A, Reason), Tag) ->
+    t(A, {Tag, Reason}).
+tag_error({ok, _}=Ok, _) ->
+    Ok;
+tag_error({error, Reason}, Tag) ->
+    {error, {Tag, Reason}}.
+
 -spec pipe([F], X) ->
     t(Ok, Error)
     when X     :: any()
@@ -76,6 +92,6 @@ lift_exn(F, Label) when is_function(F, 1) ->
         try
             {ok, F(X)}
         catch Class:Reason ->
-            {error, {Label, {Class, Reason}}}
+            tag_error({error, {Class, Reason}}, Label)
         end
     end.