The async package allows you to write sequential-looking code
that can pause, return control to R, then pick up where it left
off. Async constructs include generators, async/await blocks, and
streams (experimental as of async 0.3).
Peter Meilstrup
A generator runs until it yields a value and then stops, returning control to R until another value is requested. An async block can pause and return control to R until some data is available, then resume. Generators implement the iteror interface (which is back-compatible with iterator package.) Async blocks implement the promise interface. The new stream construct implements the channel interface, which is defined in this package.
gen(...) creates a generator (an iterator); within a generator use
yield(x) to return a value.
async(...) creates an async block (a promise); within the async
write await(x) to pause on x (another promise).
stream(...) creates a stream (an asynchronous iterator or
channel); in writing a stream you can use both await and yield.)
Theare are some global package options:
async.verbose: (default FALSE) if TRUE, coroutines will print an extremely
chatty play-by-play of what they are doing.
async.compileLevel: (0) Default compile level for new coroutines. See
description of levels under gen.
async.paranoid: (FALSE) If true, perform various time-consuming integrity
checks on the results of compilation. Meant to be enabled during certain
package tests.
async.destructive: (TRUE) If true, tear down interpreted coroutines
while building compiled replacements.
async.sendLater: (TRUE) If true, channels will send messages to listeners
in the event loop. If false, messages are sent immediately, which may be
faster but may have a higher risk of stack overflow, as well as expose
different sorts of bugs in your code.
Useful links: