Ignore outputs of side-effecting, element-handler functions.

[hope.git] / src / hope_option.erl

diff --git a/src/hope_option.erl b/src/hope_option.erl
index ad0adac..c645c53 100644 (file)
--- a/src/hope_option.erl
+++ b/src/hope_option.erl
@@ -1,27 +1,96 @@
 -module(hope_option).
 
--export_type([ t/1
-             ]).
+-behavior(hope_gen_monad).
 
--export([ put/2
-        , get/2
-        , map/2
-        ]).
+-export_type(
+    [ t/1
+    ]).
 
+-export(
+    % Generic monad interface
+    [ return/1
+    , map/2
+    , pipe/2
 
--type t(A) :: none | {some, A}.
+    % Specific to hope_option:t()
+    , return/2
+    , put/2
+    , get/2
+    , iter/2
+    , of_result/1
+    , of_undefined/1
+    , validate/2
+    ]).
 
 
-put(X, F) ->
-    case F(X)
-    of  true  -> {some, X}
-    ;   false -> none
-    end.
+-type t(A) ::
+      none
+    | {some, A}
+    .
 
 
+-spec put(A, fun((A) -> boolean())) ->
+    t(A).
+put(X, F) ->
+    return(X, F).
+
+-spec get(t(A), Default :: A) ->
+    A.
 get({some, X}, _) -> X;
 get(none     , Y) -> Y.
 
+-spec return(A) ->
+    {some, A}.
+return(X) ->
+    {some, X}.
+
+-spec return(A, fun((A) -> boolean())) ->
+    t(A).
+return(X, Condition) ->
+    case Condition(X)
+    of  true  -> {some, X}
+    ;   false -> none
+    end.
 
+-spec map(t(A), fun((A) -> (B))) ->
+    t(B).
 map({some, X}, F) -> {some, F(X)};
 map(none     , _) -> none.
+
+-spec iter(t(A), fun((A) -> (any()))) ->
+    ok.
+iter({some, X}, F) ->
+    _ = F(X),
+    ok;
+iter(none, _) ->
+    ok.
+
+-spec pipe([fun((A) -> t(B))], A) ->
+    t(B).
+pipe([], X) ->
+    return(X);
+pipe([F|Fs], X) ->
+    case F(X)
+    of  none      -> none
+    ;   {some, Y} -> pipe(Fs, Y)
+    end.
+
+-spec of_result(hope_result:t(A, _B)) ->
+    t(A).
+of_result({ok, X})    -> {some, X};
+of_result({error, _}) -> none.
+
+-spec of_undefined(undefined | A) ->
+    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.