async() should return invisibly?

[shikokuchuo]

I was creating a version of your readme example, but with an actual async download function i.e. nanonext::ncurl_aio() and using mirai to handle the external computation.

However, the promise object is returned visibly in the second coro example. This is as promises::then() returns invisibly. I propose that coro::async() can do the same?

I think this is fundamentally similar to #10. Happy to provide a PR if you'd like.

library(coro)
library(mirai)

my_async <- \(url) {
  nanonext::ncurl_aio(url) |>
    promises::then(
      \(data) {
        if (nchar(data) > 500L) {
          promises::then(
            mirai(rvest::html_text2(rvest::read_html(data)), data = data),
            \(x) cat(x, "\n")
          )
        } else {
          cat(data, "\n")
        }
      },
      onRejected = \(err) cat(conditionMessage(err), "\n")
    )
}
my_async("https://example.com/")
# Example Domain
#
# This domain is for use in illustrative examples in documents. You may use this domain in literature without prior coordination or asking for permission.
#
# More information...

my_async("https://postman-echo.com/get")
# {
#   "args": {},
#   "headers": {
#     "host": "postman-echo.com",
#     "x-request-start": "t=1723145472.652",
#     "x-forwarded-proto": "https",
#     "x-forwarded-port": "443",
#     "x-amzn-trace-id": "Root=1-66b51d00-3a00039803db97680dee8012"
#   },
#   "url": "https://postman-echo.com/get"
# } 

my_async("https://example.com/notfound")
# 404 | Not Found

my_async2 <- async(\(url) {
  
  data <- tryCatch(await(nanonext::ncurl_aio(url)), error = identity)
  
  if (inherits(data, "error"))
    return(cat(conditionMessage(data), "\n"))
  
  if (nchar(data) > 500L)
    data <- await(mirai(rvest::html_text2(rvest::read_html(data)), data = data))
  
  cat(data, "\n")
  
})

my_async2("https://example.com/")
#> <Promise [pending]>
# Example Domain
#
# This domain is for use in illustrative examples in documents. You may use this domain in literature without prior coordination or asking for permission.
#
# More information...

my_async2("https://postman-echo.com/get")
#> <Promise [pending]>
# {
#   "args": {},
#   "headers": {
#     "host": "postman-echo.com",
#     "x-request-start": "t=1723145476.118",
#     "x-forwarded-proto": "https",
#     "x-forwarded-port": "443",
#     "x-amzn-trace-id": "Root=1-66b51d04-7a9ccbdd1efef37c687c38cc"
#   },
#   "url": "https://postman-echo.com/get"
# } 

my_async2("https://example.com/notfound")
#> <Promise [pending]>
# 404 | Not Found

^{Created on 2024-08-08 with reprex v2.1.1}

Note: I've manually appended the stdout to the reprex above as the reprex package doesn't render the async output.

Btw. I think the brevity of the coro version of the code is really cool!

[lionel-]

I agree it probably makes sense to be consistent with promises here.