List.allM

1 files changed, 16 insertions, 1 deletions

diff --git a/lib/ur/list.ur b/lib/ur/list.ur
index 95d6fbc8..d28d2868 100644
--- a/lib/ur/list.ur
+++ b/lib/ur/list.ur
@@ -319,7 +319,7 @@ fun filterM [m] (_ : monad m) [a] (p : a -> m bool) =
         filterM' []
     end
 
-fun all [m] f =
+fun all [a] f =
     let
         fun all' ls =
             case ls of
@@ -329,6 +329,21 @@ fun all [m] f =
         all'
     end
 
+fun allM [m] (_ : monad m) [a] f =
+    let
+        fun all' ls =
+            case ls of
+                [] => return True
+              | x :: ls =>
+                b <- f x;
+                if b then
+                    all' ls
+                else
+                    return False
+    in
+        all'
+    end
+
 fun app [m] (_ : monad m) [a] f =
     let
         fun app' ls =