-module(hope_result).
--export_type([ t/2
- ]).
+-behavior(hope_gen_monad).
--export([ pipe/2
- ]).
+-export_type(
+ [ t/2
+ ]).
+-export(
+ [ return/1
+ , map/2
+ , pipe/2
+ , lift_exn/1
+ , lift_exn/2
+ ]).
--type t(A, B) :: {ok, A} | {error, B}.
+-type t(A, B) ::
+ {ok, A}
+ | {error, B}
+ .
-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.