eager: Create an eager future whose value will be resolved immediately

Description

An eager future is a future that uses eager evaluation, which means that its value is computed and resolved immediately, which is how regular 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

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

Arguments

expr

An R expression.

envir

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

substitute

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

globals

A logical, a character vector, or a named list for controlling how globals are handled. For details, see below section. This argument can be specified via the ... arguments for future() and futureCall().

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

An EagerFuture.

transparent futures

Transparent futures are eager 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 an eager future is not to call this function directly, but to register it via plan(eager) such that it becomes the default mechanism for all futures. After this future() and %<-% will create eager futures.

Examples

Run this code

## Use eager futures
plan(eager)

## A global variable
a <- 0

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

## Since 'a' is a global variable in _eager_ future 'f',
## it already has been resolved, 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)

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