Define and implement a generic monad behavior.

[hope.git] / src / hope_result.erl

diff --git a/src/hope_result.erl b/src/hope_result.erl
index 06f1eeb..1114197 100644 (file)
--- a/src/hope_result.erl
+++ b/src/hope_result.erl
@@ -1,11 +1,17 @@
 -module(hope_result).
 
+-behavior(hope_monad).
+
 -export_type(
     [ t/2
     ]).
 
 -export(
-    [ pipe/2
+    [ return/1
+    , map/2
+    , pipe/2
+    , lift_exn/1
+    , lift_exn/2
     ]).
 
 
@@ -15,9 +21,61 @@
     .
 
 
-pipe([]    , X) -> X;
+-spec return(A) ->
+    {ok, A}.
+return(X) ->
+    {ok, X}.
+
+-spec map(t(A, Error), fun((A) -> (B))) ->
+    t(B, Error).
+map({ok, X}, F) ->
+    {ok, F(X)};
+map({error, _}=Error, _) ->
+    Error.
+
+-spec pipe([F], X) ->
+    t(Ok, Error)
+    when X     :: any()
+       , Ok    :: any()
+       , Error :: any()
+       , F     :: fun((X) -> t(Ok, Error))
+       .
+pipe([], X) ->
+    {ok, X};
 pipe([F|Fs], X) ->
     case F(X)
     of  {error, _}=E -> E
     ;   {ok, Y}      -> pipe(Fs, Y)
     end.
+
+-spec lift_exn(F) -> G
+    when F     :: fun((A)-> B)
+       , G     :: fun((A)-> t(B, {Class, Reason :: any()}))
+       , Class :: error
+                | exit
+                | throw
+       .
+lift_exn(F) when is_function(F, 1) ->
+    fun(X) ->
+        try
+            {ok, F(X)}
+        catch Class:Reason ->
+            {error, {Class, Reason}}
+        end
+    end.
+
+-spec lift_exn(F, Label) -> G
+    when F     :: fun((A)-> B)
+       , G     :: fun((A)-> t(B, {Label, {Class, Reason :: any()}}))
+       , Class :: error
+                | exit
+                | throw
+       .
+lift_exn(F, Label) when is_function(F, 1) ->
+    fun(X) ->
+        try
+            {ok, F(X)}
+        catch Class:Reason ->
+            {error, {Label, {Class, Reason}}}
+        end
+    end.