Promises Integration

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

A ‘mirai’ may be piped directly using the promise pipe &...>%, which implicitly calls as.promise() on the ‘mirai’.

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)
library(promises)

env <- new.env()

m <- mirai({Sys.sleep(1); "hello"})
p <- as.promise(m)$then(function(x) env$res <- x)

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

# after returning to the top level prompt:
env$res
#> [1] "hello"