List.mapXi

2 files changed, 12 insertions, 0 deletions

diff --git a/lib/ur/list.ur b/lib/ur/list.ur
index 2679d877..35440de2 100644
--- a/lib/ur/list.ur
+++ b/lib/ur/list.ur
@@ -133,6 +133,16 @@ fun mapX [a] [ctx ::: {Unit}] f =
         mapX'
     end
 
+fun mapXi [a] [ctx ::: {Unit}] f =
+    let
+        fun mapX' i ls =
+            case ls of
+                [] => <xml/>
+              | x :: ls => <xml>{f i x}{mapX' (i + 1) ls}</xml>
+    in
+        mapX' 0
+    end
+
 fun mapM [m ::: (Type -> Type)] (_ : monad m) [a] [b] f =
     let
         fun mapM' acc ls =
diff --git a/lib/ur/list.urs b/lib/ur/list.urs
index 00bb5b48..851d74bc 100644
--- a/lib/ur/list.urs
+++ b/lib/ur/list.urs
@@ -26,6 +26,8 @@ val mapi : a ::: Type -> b ::: Type -> (int -> a -> b) -> t a -> t b
 
 val mapX : a ::: Type -> ctx ::: {Unit} -> (a -> xml ctx [] []) -> t a -> xml ctx [] []
 
+val mapXi : a ::: Type -> ctx ::: {Unit} -> (int -> a -> xml ctx [] []) -> t a -> xml ctx [] []
+
 val mapM : m ::: (Type -> Type) -> monad m -> a ::: Type -> b ::: Type
            -> (a -> m b) -> t a -> m (t b)