Some standard library additions from Edward Z. Yang

6 files changed, 35 insertions, 0 deletions

diff --git a/lib/ur/list.ur b/lib/ur/list.ur
index 2d5addc9..bce5335e 100644
--- a/lib/ur/list.ur
+++ b/lib/ur/list.ur
@@ -424,3 +424,16 @@ fun drop [a] (n : int) (xs : list a) : list a =
 
 fun splitAt [a] (n : int) (xs : list a) : list a * list a =
     (take n xs, drop n xs)
+
+fun mapXiM [m ::: Type -> Type] (_ : monad m) [a] [ctx ::: {Unit}] (f : int -> a -> m (xml ctx [] [])) : t a -> m (xml ctx [] []) =
+    let
+        fun mapXiM' i ls =
+            case ls of
+                [] => return <xml/>
+              | x :: ls =>
+                this <- f i x;
+                rest <- mapXiM' (i+1) ls;
+                return <xml>{this}{rest}</xml>
+    in
+        mapXiM' 0
+    end
diff --git a/lib/ur/list.urs b/lib/ur/list.urs
index 15204590..b26c9ad9 100644
--- a/lib/ur/list.urs
+++ b/lib/ur/list.urs
@@ -36,6 +36,8 @@ val mapPartialM : m ::: (Type -> Type) -> monad m -> a ::: Type -> b ::: Type ->
 val mapXM : m ::: (Type -> Type) -> monad m -> a ::: Type -> ctx ::: {Unit}
             -> (a -> m (xml ctx [] [])) -> t a -> m (xml ctx [] [])
 
+val mapXiM : m ::: (Type -> Type) -> monad m -> a ::: Type -> ctx ::: {Unit} -> (int -> a -> m (xml ctx [] [])) -> t a -> m (xml ctx [] [])
+
 val filter : a ::: Type -> (a -> bool) -> t a -> t a
 
 val exists : a ::: Type -> (a -> bool) -> t a -> bool
diff --git a/lib/ur/monad.ur b/lib/ur/monad.ur
index 3d03298e..ab7742fe 100644
--- a/lib/ur/monad.ur
+++ b/lib/ur/monad.ur
@@ -12,6 +12,8 @@ fun mp [m] (_ : monad m) [a] [b] f m =
     v <- m;
     return (f v)
 
+val liftM = @@mp
+
 fun foldR [K] [m] (_ : monad m) [tf :: K -> Type] [tr :: {K} -> Type]
           (f : nm :: Name -> t :: K -> rest :: {K}
                -> [[nm] ~ rest] =>
@@ -122,3 +124,8 @@ fun appR3 [K] [m] (_ : monad m) [tf1 :: K -> Type] [tf2 :: K -> Type] [tf3 :: K
          f [nm] [t] r1.nm r2.nm r3.nm)
      (fn _ _ _ => return ())
      fl
+
+fun liftM2 [m ::: Type -> Type] (_ : monad m) [a] [b] [c] (f : a -> b -> c) (mx : m a) (my : m b) : m c =
+    x <- mx;
+    y <- my;
+    return (f x y)
diff --git a/lib/ur/monad.urs b/lib/ur/monad.urs
index d07d5026..ce823f4a 100644
--- a/lib/ur/monad.urs
+++ b/lib/ur/monad.urs
@@ -7,6 +7,13 @@ val ignore : m ::: (Type -> Type) -> monad m -> t ::: Type
 val mp : m ::: (Type -> Type) -> monad m -> a ::: Type -> b ::: Type
          -> (a -> b) -> m a -> m b
 
+val liftM : m ::: (Type -> Type) -> monad m -> a ::: Type -> b ::: Type
+            -> (a -> b) -> m a -> m b
+(* Haskell-style synonym for [mp] *)
+
+val liftM2 : m ::: (Type -> Type) -> monad m -> a ::: Type -> b ::: Type -> c ::: Type
+             -> (a -> b -> c) -> m a -> m b -> m c
+
 val foldR : K --> m ::: (Type -> Type) -> monad m
             -> tf :: (K -> Type)
             -> tr :: ({K} -> Type)
diff --git a/tests/monad.urp b/tests/monad.urp
new file mode 100644
index 00000000..91523ca2
--- /dev/null
+++ b/tests/monad.urp
@@ -0,0 +1,3 @@
+$/monad
+$/list
+monadTest
diff --git a/tests/monadTest.ur b/tests/monadTest.ur
new file mode 100644
index 00000000..16a10f74
--- /dev/null
+++ b/tests/monadTest.ur
@@ -0,0 +1,3 @@
+val x : transaction int = Monad.liftM2 plus (return 1) (return 2)
+
+val x : transaction xbody = List.mapXiM (fn i x => return <xml><li>{[i]} = {[x]}</li></xml>) (1 :: 2 :: [])