add foldr

prelude.ld

@@ -228,6 +228,22 @@ fn fold {
 	}
 }
 
+
+fn foldr {
+	"Folds a list, right-associative."
+	(f as :fn, []) -> []
+	(f as :fn, xs as :list) -> fold (f, xs, f ())
+	(f as :fn, [], root) -> []
+	(f as :fn, xs as :list, root) -> loop (root, first (xs), rest (xs)) with {
+		(prev, curr, []) -> f (curr, prev)
+		(prev, curr, remaining) -> recur (
+			f (curr, prev)
+			first (remaining)
+			rest (remaining)
+		)
+	}
+}
+
 & TODO: optimize these with base :conj!
 fn map {
 	"Maps a function over a list: returns a new list with elements that are the result of applying the function to each element in the original list. E.g., `map ([1, 2, 3], inc) &=> [2, 3, 4]`."
@@ -1359,6 +1375,7 @@ pkg Prelude {
 	floor & math
 	fn? & functions
 	fold & lists
+	foldr & lists
 	forward! & turtles
 	get & dicts
 	goto! & turtles