List library additions; fix another substructure unification bug

2 files changed, 32 insertions, 0 deletions

diff --git a/lib/ur/list.ur b/lib/ur/list.ur
index 0776ff30..0aae9010 100644
--- a/lib/ur/list.ur
+++ b/lib/ur/list.ur
@@ -122,3 +122,31 @@ fun foldlMap [a] [b] [c] f =
     in
         fold []
     end
+
+fun assoc [a] [b] (_ : eq a) (x : a) =
+    let
+        fun assoc' ls =
+            case ls of
+                [] => None
+              | (y, z) :: ls =>
+                if x = y then
+                    Some z
+                else
+                    assoc' ls
+    in
+        assoc'
+    end
+
+fun search [a] [b] f =
+    let
+        fun search' ls =
+            case ls of
+                [] => None
+              | x :: ls =>
+                case f x of
+                    None => search' ls
+                  | v => v
+    in
+        search'
+    end
+
diff --git a/lib/ur/list.urs b/lib/ur/list.urs
index 92589508..1b80a9d3 100644
--- a/lib/ur/list.urs
+++ b/lib/ur/list.urs
@@ -26,3 +26,7 @@ val exists : a ::: Type -> (a -> bool) -> t a -> bool
 
 val foldlMap : a ::: Type -> b ::: Type -> c ::: Type
                -> (a -> b -> c * b) -> b -> t a -> t c * b
+
+val assoc : a ::: Type -> b ::: Type -> eq a -> a -> t (a * b) -> option b
+
+val search : a ::: Type -> b ::: Type -> (a -> option b) -> t a -> option b