Define and implement a generic monad behavior.

[hope.git] / src / hope_option.erl

diff --git a/src/hope_option.erl b/src/hope_option.erl
index ab6eab7..180c416 100644 (file)
--- a/src/hope_option.erl
+++ b/src/hope_option.erl
@@ -1,5 +1,6 @@
 -module(hope_option).
 
+-behavior(hope_monad).
 
 -export_type(
     [ t/1
@@ -8,8 +9,10 @@
 -export(
     [ put/2
     , get/2
+    , return/1
     , map/2
     , iter/2
+    , pipe/2
     , of_result/1
     ]).
 
@@ -33,6 +36,11 @@ put(X, F) ->
 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)};
@@ -43,6 +51,16 @@ map(none     , _) -> none.
 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};