From 8a0dced7d9344b92ae6053554051e85a1e5208c7 Mon Sep 17 00:00:00 2001
From: Joe Cheng <joe@posit.co>
Date: Tue, 26 Nov 2024 15:00:33 -0800
Subject: [PATCH] Add `async_gen()` (async version of `gen()`)

---
 NAMESPACE              |  1 +
 R/async.R              | 25 +++++++++++++++++++++++--
 man/async_generator.Rd | 19 ++++++++++++++++++-
 3 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/NAMESPACE b/NAMESPACE
index 9939ed9..15a6bd5 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -9,6 +9,7 @@ S3method(print,coro_generator_instance)
 export(as_iterator)
 export(async)
 export(async_collect)
+export(async_gen)
 export(async_generator)
 export(async_ops)
 export(async_sleep)
diff --git a/R/async.R b/R/async.R
index b827d03..b58c61d 100644
--- a/R/async.R
+++ b/R/async.R
@@ -76,7 +76,7 @@ await <- function(x) {
 #' @export
 async_sleep <- function(seconds) {
   promises::promise(function(resolve, reject) {
-    later::later(~ resolve(NULL) , delay = seconds)
+    later::later(~ resolve(NULL), delay = seconds)
   })
 }
 
@@ -116,13 +116,34 @@ async_sleep <- function(seconds) {
 #' # Example usage:
 #' if (interactive()) {
 #'   library(magrittr)
-#'   generate_stream(1:3) %>% async_map(`*`, 2) %>% async_collect()
+#'   generate_stream(1:3) %>%
+#'     async_map(`*`, 2) %>%
+#'     async_collect()
+#' }
+#'
+#' # coro provides a short syntax `async_gen()` for creating one-off
+#' # generator _instances_. It is handy to adapt existing iterators:
+#' numbers <- generate_stream(1:10)
+#' odds <- async_gen(for (x in await_each(numbers)) if (x %% 2 != 0) yield(x))
+#' squares <- async_gen(for (x in await_each(odds)) yield(x^2))
+#' greetings <- async_gen(for (x in await_each(squares)) yield(paste("Hey", x)))
+#' if (interactive()) {
+#'   async_collect(greetings) %>% promises::then(print)
 #' }
 #' @export
 async_generator <- function(fn) {
   assert_lambda(substitute(fn))
   generator0(fn, type = "async_generator")
 }
+
+#' @rdname async_generator
+#' @param expr A yielding expression.
+#' @export
+async_gen <- function(expr) {
+  fn <- new_function(NULL, substitute(expr), caller_env())
+  generator0(fn, type = "async_generator")()
+}
+
 #' @rdname async_generator
 #' @inheritParams await
 #' @export
diff --git a/man/async_generator.Rd b/man/async_generator.Rd
index 9c3a2c0..1fa7608 100644
--- a/man/async_generator.Rd
+++ b/man/async_generator.Rd
@@ -2,17 +2,22 @@
 % Please edit documentation in R/async.R
 \name{async_generator}
 \alias{async_generator}
+\alias{async_gen}
 \alias{await_each}
 \title{Construct an async generator}
 \usage{
 async_generator(fn)
 
+async_gen(expr)
+
 await_each(x)
 }
 \arguments{
 \item{fn}{An anonymous function describing an async generator
 within which \code{await()} calls are allowed.}
 
+\item{expr}{A yielding expression.}
+
 \item{x}{An awaitable value, i.e. a \link[promises:promise]{promise}.}
 }
 \value{
@@ -44,7 +49,19 @@ async_map <- async_generator(function(.i, .fn, ...) {
 # Example usage:
 if (interactive()) {
   library(magrittr)
-  generate_stream(1:3) \%>\% async_map(`*`, 2) \%>\% async_collect()
+  generate_stream(1:3) \%>\%
+    async_map(`*`, 2) \%>\%
+    async_collect()
+}
+
+# coro provides a short syntax `async_gen()` for creating one-off
+# generator _instances_. It is handy to adapt existing iterators:
+numbers <- generate_stream(1:10)
+odds <- async_gen(for (x in await_each(numbers)) if (x \%\% 2 != 0) yield(x))
+squares <- async_gen(for (x in await_each(odds)) yield(x^2))
+greetings <- async_gen(for (x in await_each(squares)) yield(paste("Hey", x)))
+if (interactive()) {
+  async_collect(greetings) \%>\% promises::then(print)
 }
 }
 \seealso{