metaAction {shinymeta}

Run/capture non-reactive code for side effects

Description

Most apps start out with setup code that is non-reactive, such as library() calls, loading of static data into local variables, or source-ing of supplemental R scripts. metaAction provides a convenient way to run such code for its side effects (including declaring new variables) while making it easy to export that code using expandChain(). Note that metaAction executes code directly in the env environment (which defaults to the caller's environment), so any local variables that are declared in the expr will be available outside of metaAction as well.

Usage

metaAction(expr, env = parent.frame(), quoted = FALSE)

Arguments

expr

A code expression that will immediately be executed (before the call to metaAction returns), and also stored for later retrieval (i.e. meta mode).

env

An environment.

quoted

Is the expression quoted? This is useful when you want to use an expression that is stored in a variable; to do so, it must be quoted with quote().

Value

A function that, when called in meta mode (i.e. inside expandChain()), will return the code in quoted form. If this function is ever called outside of meta mode, it throws an error, as it is definitely being called incorrectly.

Examples

setup <- metaAction({
  library(stats)

  "# Set the seed to ensure repeatable randomness"
  set.seed(100)

  x <- 1
  y <- 2
})

# The action has executed
print(x)
print(y)

# And also you can emit the code
expandChain(
  setup()
)