Push promises method performance (shikokuchuo#161)

* use underlying promises functions

* use .unresolved()

* advance version

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: mirai
 Type: Package
 Title: Minimalist Async Evaluation Framework for R
-Version: 1.2.0.9029
+Version: 1.2.0.9030
 Description: Designed for simplicity, a 'mirai' evaluates an R expression
     asynchronously in a parallel process, locally or distributed over the
     network, with the result automatically available upon completion. Modern

NEWS.md

@@ -1,4 +1,4 @@
-# mirai 1.2.0.9029 (development)
+# mirai 1.2.0.9030 (development)
 
 #### New Features
 

R/promises.R

@@ -68,22 +68,23 @@ as.promise.mirai <- function(x) {
 
   if (is.null(promise)) {
 
-    if (unresolved(x)) {
-      promise <- promises::then(
-        promises::promise(
-          function(resolve, reject) .keep(x, environment())
-        ),
+    promise <- if (.unresolved(x)) {
+      promises::promise(
+        function(resolve, reject) .keep(x, environment())
+      )$then(
         onFulfilled = function(value)
           if (is_error_value(value) && !is_mirai_interrupt(value))
             stop(if (is_mirai_error(value)) value else nng_error(value)) else
               value
       )
-
     } else {
-      value <- .subset2(x, "value")
-      promise <- if (is_error_value(value) && !is_mirai_interrupt(value))
-        promises::promise_reject(if (is_mirai_error(value)) value else nng_error(value)) else
-          promises::promise_resolve(value)
+      value <- collect_aio(x)
+      promises::promise(
+        function(resolve, reject)
+          if (is_error_value(value) && !is_mirai_interrupt(value))
+            reject(value) else
+              resolve(value)
+      )
     }
 
     assign("promise", promise, x)