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-rw-r--r--lib/ur/monad.ur13
1 files changed, 13 insertions, 0 deletions
diff --git a/lib/ur/monad.ur b/lib/ur/monad.ur
index 356173fd..d6690839 100644
--- a/lib/ur/monad.ur
+++ b/lib/ur/monad.ur
@@ -34,6 +34,19 @@ fun foldR2 [K] [m] (_ : monad m) [tf1 :: K -> Type] [tf2 :: K -> Type] [tr :: {K
(fn _ _ => return i)
[_] fl
+fun foldR3 [K] [m] (_ : monad m) [tf1 :: K -> Type] [tf2 :: K -> Type] [tf3 :: K -> Type] [tr :: {K} -> Type]
+ (f : nm :: Name -> t :: K -> rest :: {K}
+ -> [[nm] ~ rest] =>
+ tf1 t -> tf2 t -> tf3 t -> tr rest -> m (tr ([nm = t] ++ rest)))
+ (i : tr []) [r :: {K}] (fl : folder r) =
+ Top.fold [fn r :: {K} => $(map tf1 r) -> $(map tf2 r) -> $(map tf3 r) -> m (tr r)]
+ (fn [nm :: Name] [t :: K] [rest :: {K}] [[nm] ~ rest]
+ (acc : _ -> _ -> _ -> m (tr rest)) r1 r2 r3 =>
+ acc' <- acc (r1 -- nm) (r2 -- nm) (r3 -- nm);
+ f [nm] [t] [rest] ! r1.nm r2.nm r3.nm acc')
+ (fn _ _ _ => return i)
+ [_] fl
+
fun mapR [K] [m] (_ : monad m) [tf :: K -> Type] [tr :: K -> Type]
(f : nm :: Name -> t :: K -> tf t -> m (tr t)) =
@@foldR [m] _ [tf] [fn r => $(map tr r)]