Implement hope_option:of_undefined/1

[hope.git] / src / hope_option.erl

diff --git a/src/hope_option.erl b/src/hope_option.erl
index ad0adac..529158d 100644 (file)
--- a/src/hope_option.erl
+++ b/src/hope_option.erl
@@ -1,27 +1,73 @@
 -module(hope_option).
 
--export_type([ t/1
-             ]).
+-behavior(hope_monad).
 
--export([ put/2
-        , get/2
-        , map/2
-        ]).
+-export_type(
+    [ t/1
+    ]).
 
+-export(
+    [ put/2
+    , get/2
+    , return/1
+    , map/2
+    , iter/2
+    , pipe/2
+    , of_result/1
+    , of_undefined/1
+    ]).
 
--type t(A) :: none | {some, A}.
 
+-type t(A) ::
+      none
+    | {some, A}
+    .
 
+
+-spec put(A, fun((A) -> boolean())) ->
+    t(A).
 put(X, F) ->
     case F(X)
     of  true  -> {some, X}
     ;   false -> none
     end.
 
-
+-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 map(t(A), fun((A) -> (B))) ->
+    t(B).
 map({some, X}, F) -> {some, F(X)};
 map(none     , _) -> none.
+
+-spec iter(t(A), fun((A) -> (ok))) ->
+    ok.
+iter({some, X}, F) -> ok = F(X);
+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}.