From d1a5e047fe7c290cd61afa02604273f9190ef715 Mon Sep 17 00:00:00 2001
From: Fardale <fardale+git@crans.org>
Date: Fri, 24 Jan 2020 22:57:25 +0100
Subject: [PATCH] feat(CCResult): add get_lazy

fixes #285
---
 src/core/CCResult.ml  | 9 +++++++++
 src/core/CCResult.mli | 4 ++++
 2 files changed, 13 insertions(+)

diff --git a/src/core/CCResult.ml b/src/core/CCResult.ml
index 2b4dbd35..b30659b0 100644
--- a/src/core/CCResult.ml
+++ b/src/core/CCResult.ml
@@ -117,6 +117,15 @@ let get_or_failwith = function
   try ignore @@ get_or_failwith (Error "e"); false with Failure msg -> msg = "e"
 *)
 
+let get_lazy default_fn x = match x with
+  | Ok x -> x
+  | Error e -> default_fn e
+
+(*$= get_lazy
+  (get_lazy (fun _ -> 2) (Ok 1)) (1)
+  (get_lazy (fun _ -> 2) (Error "error")) (2)
+*)
+
 let map_or f e ~default = match e with
   | Ok x -> f x
   | Error _ -> default
diff --git a/src/core/CCResult.mli b/src/core/CCResult.mli
index 1259ca26..e6b2cb30 100644
--- a/src/core/CCResult.mli
+++ b/src/core/CCResult.mli
@@ -101,6 +101,10 @@ val get_or_failwith : ('a, string) t -> 'a
     @raise Failure with [msg] if [e = Error msg].
     @since 2.4 *)
 
+val get_lazy : ('b -> 'a) -> ('a, 'b) t -> 'a
+(** [get_lazy default_fn x] unwraps [x], but if [x = Error e] it returns [default_fr e] instead.
+    @since NEXT_RELEASE *)
+
 val map_or : ('a -> 'b) ->  ('a, 'c) t -> default:'b -> 'b
 (** [map_or f e ~default] returns [f x] if [e = Ok x], [default] otherwise. *)