add news item + document

NEWS.md

@@ -1,5 +1,8 @@
 # coro (development version)
 
+* Async functions created by `coro::async()` now return their
+  `promises::promise()` invisibly (#46, @shikokuchuo).
+
 # coro 1.0.4
 
 * Internal fix for R-devel.

R/async.R

@@ -27,7 +27,7 @@
 #'
 #' @param fn An anonymous function within which `await()` calls are
 #'   allowed.
-#' @return A function that returns a [promises::promise()].
+#' @return A function that returns a [promises::promise()] invisibly.
 #'
 #' @seealso [async_generator()] and [await_each()];
 #'   [coro_debug()] for step-debugging.
@@ -75,9 +75,11 @@ await <- function(x) {
 #' @return A chainable promise.
 #' @export
 async_sleep <- function(seconds) {
-  promises::promise(function(resolve, reject) {
-    later::later(~ resolve(NULL) , delay = seconds)
-  })
+  invisible(
+    promises::promise(function(resolve, reject) {
+      later::later(~ resolve(NULL) , delay = seconds)
+    })
+  )
 }
 
 #' Construct an async generator