future (version 1.3.0)

sequential: Create a sequential future whose value will be in the current R session

Description

A sequential future is a future that is evaluated sequentially in the current R session similarly to how R expressions are evaluated in R. The only difference to R itself is that globals are validated by default just as for all other types of futures in this package.

Usage

sequential(expr, envir = parent.frame(), substitute = TRUE, lazy = FALSE,
  seed = NULL, globals = TRUE, local = TRUE, earlySignal = FALSE,
  label = NULL, ...)
transparent(expr, envir = parent.frame(), substitute = TRUE, lazy = FALSE,
  seed = NULL, globals = FALSE, local = FALSE, earlySignal = TRUE,
  label = NULL, ...)
eager(expr, envir = parent.frame(), substitute = TRUE, lazy = FALSE,
  seed = NULL, globals = TRUE, local = TRUE, earlySignal = FALSE,
  label = NULL, ...)
lazy(expr, envir = parent.frame(), substitute = TRUE, lazy = TRUE,
  seed = NULL, globals = TRUE, local = TRUE, earlySignal = FALSE,
  label = NULL, ...)

Arguments

expr

An R expression to be evaluated.

envir

The environment from where global objects should be identified. Depending on the future strategy (the evaluator), it may also be the environment in which the expression is evaluated.

substitute

If TRUE, argument expr is substitute():ed, otherwise not.

lazy

Specifies whether a future should be resolved lazily or eagerly. The default is eager evaluation (except when the deprecated plan(lazy) is used).

seed

(optional) A L'Ecuyer-CMRG RNG seed.

globals

A logical, a character vector, or a named list for controlling how globals are handled. For details, see below section.

local

If TRUE, the expression is evaluated such that all assignments are done to local temporary environment, otherwise the assignments are done in the calling environment.

earlySignal

Specified whether conditions should be signaled as soon as possible or not.

label

An optional character string label attached to the future.

...

Additional arguments passed to the "evaluator".

Value

A SequentialFuture.

transparent futures

Transparent futures are sequential futures configured to emulate how R evaluates expressions as far as possible. For instance, errors and warnings are signaled immediately and assignments are done to the calling environment (without local() as default for all other types of futures). This makes transparent futures ideal for troubleshooting, especially when there are errors.

Details

The preferred way to create a sequential future is not to call these functions directly, but to register them via plan(sequential) such that it becomes the default mechanism for all futures. After this future() and %<-% will create sequential futures.

Examples

## Use sequential futures
plan(sequential)

## A global variable
a <- 0

## Create a sequential future
f <- future({
  b <- 3
  c <- 2
  a * b * c
})

## Since 'a' is a global variable in future 'f' which
## is eagerly resolved (default), this global has already
## been resolved / incorporated, and any changes to 'a'
## at this point will _not_ affect the value of 'f'.
a <- 7
print(a)

v <- value(f)
print(v)
stopifnot(v == 0)