mirai - Promises Integration

Promises Integration

{mirai} supplies its own as.promise() method, allowing it to be used as a promise from the promises package.

These promises are innovative, event-driven promises, developed in collaboration with Joe Cheng.

• Do not require each promise to be polled for completion by a later loop like other promises.
• Instead, promise actions are automatically queued for execution as soon as each ‘mirai’ resolves.
• Allows for much higher responsiveness (lower latency) and massive scalability (situations with thousand of promises or more).

A ‘mirai’ may be piped directly using the promise pipe &...>%, which implicitly calls as.promise() on the ‘mirai’. Similarly all promise-aware functions such as promises::then() or shiny::ExtendedTask$new() which take a promise can also take a ‘mirai’ (using promises >= 1.3.0).

Alternatively, it may be converted into a promise by as.promise(), which then allows using the methods $then(), $finally() etc.

The following example outputs “hello” to the console after one second when the ‘mirai’ resolves.

library(mirai)
library(promises)

p <- mirai({Sys.sleep(1); "hello"}) %...>% cat()
p
#> <Promise [pending]>

It is possible to both access a ‘mirai’ value at $data and to use a promise for enacting a side effect (assigning the value to an environment in the example below).

library(mirai)

env <- new.env()

m <- mirai({
  Sys.sleep(1)
  "hello"
})

promises::then(m, function(x) env$res <- x)

call_mirai(m)$data
#> [1] "hello"

After returning to the top level prompt:

env$res
#> [1] "hello"