Rserve (version 1.8-15)

Rserve.eval: Evaluate expressions in a REPL-like fashion

Description

Rserve.eval evaluates a given expression in a way that is very close to the behavior on the console Read/Evaluate/Print Loop (REPL). Among other things this means printing the result of each expression if visible. The function is guaranteed to not raise an error and in case of an error it returns an object of class Rserve-eval-error with details including the error and the stack trace.

Usage

Rserve.eval(what, where = .GlobalEnv, last.value = FALSE, exp.value = FALSE,
            context = NULL, handlers = list(error=.save.condition))

Value

If the evaluation triggered an error, the result is an object of class

Rserve-eval-error with components:

error

character, error message

traceback

list of contexts in the traceback

expression

if what contains multiple expressions then this will be either an index to the expression that caused the error (exp.value=FALSE) or the actual expression (otherwise).

context

current Rserve context, NULL if none has been set

condition

if any condition has been saved via .save.condition (which is the default) then on error the captured condition object is stored here, NULL otherwise

If the evaluation finished without an error then the result is either

TRUE if last.value=FALSE or the value of the last expression otherwise.

Arguments

what

expressions to evaluate

where

environment to evaluate in

last.value

logical, if TRUE then the result of the evaluation is returned, otherwise the evaluation is only performed for its side-efects and returns TRUE instead.

exp.value

logical, it TRUE then an error object will include the actual expression that triggered the error, otherwise it will only store the index of the expression in what.

context

optional object that will be used as the Rserve context for the duration of the evaluation (see Rserve.context).

handlers

optional named list of calling handlers to register for the duration of the evaluation. The default is to register an error handlers which stores the error condition so it can be reported in the result - see below.

Author

Simon Urbanek

Details

If what contains one or more expressions, they are evaluated one by one while printing the result of each if visible. Upon error subsequent expressions are not evaluated. If what is not an expression then the only a single evaluation of what is performed and the result is not printed.

The main purpose of this function is to implement console front-ends where the front-end uses parse() + Rserve.eval() to simulate the action of a GUI. Because the function returns in all circumstances it allows clients to rely on a well-define messaging behavior.

Examples

  g <- function() stop("foo")
  f <- function() g()
  (Rserve.eval(expression(f())))
  (Rserve.eval(parse(text="1:5\n1+1")))
  (Rserve.eval(quote(1+1), last.value=TRUE))

  error_with_condition = function(object = NULL) {
    cond = errorCondition("this is a custom error with condition",
                          object = object, 
                          class = "CustomError")
    stop(cond)
  }
  str(Rserve.eval(quote(error_with_condition("hello")), last.value = TRUE))