List.find

2 files changed, 16 insertions, 0 deletions

diff --git a/lib/ur/list.ur b/lib/ur/list.ur
index 32a9679c..2679d877 100644
--- a/lib/ur/list.ur
+++ b/lib/ur/list.ur
@@ -206,6 +206,20 @@ fun foldlMap [a] [b] [c] f =
         fold []
     end
 
+fun find [a] f =
+    let
+        fun find' ls =
+            case ls of
+                [] => None
+              | x :: ls =>
+                if f x then
+                    Some x
+                else
+                    find' ls
+    in
+        find'
+    end
+
 fun search [a] [b] f =
     let
         fun search' ls =
diff --git a/lib/ur/list.urs b/lib/ur/list.urs
index dc8fdeba..00bb5b48 100644
--- a/lib/ur/list.urs
+++ b/lib/ur/list.urs
@@ -44,6 +44,8 @@ val foldlM : m ::: (Type -> Type) -> monad m -> a ::: Type -> b ::: Type
 val foldlMap : a ::: Type -> b ::: Type -> c ::: Type
                -> (a -> b -> c * b) -> b -> t a -> t c * b
 
+val find : a ::: Type -> (a -> bool) -> t a -> option a
+
 val search : a ::: Type -> b ::: Type -> (a -> option b) -> t a -> option b
 
 val all : a ::: Type -> (a -> bool) -> t a -> bool