async/non-blocking programming in R with `mirai`

async_mirai.R

### Usage:

# a = 1; b = 2
# my_result <- eval.async(a+b)
### when mirai::unresolved(my_result) == FALSE
### you can use my_result$data

### do.call.async can be used like do.call

eval.async <-
  function(.expr,
           .list_of_objects = mget(ls(envir=parent.frame(),all.names=TRUE),
                                   envir=parent.frame()),
           .loaded_packages = sub("package:", "",
                                  grep("package:",search(),value=TRUE), 
                                  fixed=TRUE)) {
    force(.list_of_objects)
    eval(bquote(mirai::mirai({
      local(for (package in .(.loaded_packages))
        library(package, character.only = TRUE))
      list2env(.(.list_of_objects), envir = .GlobalEnv)
      .(substitute(.expr))
    })))
  }

do.call.async <- function(what, args)
  eval(bquote(eval.async(do.call(.(what),.(args)))))