Implement hope_option:validate/2

[hope.git] / src / hope_option.erl

diff --git a/src/hope_option.erl b/src/hope_option.erl
index 7a87438..996e342 100644 (file)
--- a/src/hope_option.erl
+++ b/src/hope_option.erl
@@ -7,15 +7,19 @@
     ]).
 
 -export(
-    [ put/2
-    , get/2
-    , return/1
-    , return/2
+    % Generic monad interface
+    [ return/1
     , map/2
-    , iter/2
     , pipe/2
+
+    % Specific to hope_option:t()
+    , return/2
+    , put/2
+    , get/2
+    , iter/2
     , of_result/1
     , of_undefined/1
+    , validate/2
     ]).
 
 
@@ -77,3 +81,13 @@ of_result({error, _}) -> none.
     t(A).
 of_undefined(undefined) -> none;
 of_undefined(X)         -> {some, X}.
+
+-spec validate(t(A), fun((A) -> boolean())) ->
+    t(A).
+validate(none, _) ->
+    none;
+validate({some, X}=T, F) ->
+    case F(X)
+    of  false -> none
+    ;   true  -> T
+    end.