R avoiding "restarting interrupted promise evaluation" warning

Question

Problem

It seems that within a function, when you evaluate an expression that yields an error more than once, you get the warning restarting interrupted promise evaluation. For instance:

foo <- function() stop("Foo error") bar <- function(x) {     try(x)     x } bar(foo()) 

yields

Error in foo() : Foo error Error in foo() : Foo error In addition: Warning message: In bar(foo()) : restarting interrupted promise evaluation 

How to avoid this warning and deal with it properly?

Background

Especially with operations like writing to a database, you might encounter locking errors that require you to retry your operation a few times. Hence I'm creating a wrapper around tryCatch that re-evaluates an expression up to n times until successful:

tryAgain <- function(expr, n = 3) {     success <- T     for (i in 1:n) {         res <- tryCatch(expr,             error = function(e) {                 print(sprintf("Log error to file: %s", conditionMessage(e)))                 success <<- F                 e             }         )         if (success) break     }     res } 

However, I'm getting loads of restarting interrupted promise evaluation messages:

>   tryAgain(foo()) [1] "Log error to file: Foo error" [1] "Log error to file: Foo error" [1] "Log error to file: Foo error" <simpleError in foo(): Foo error> Warning messages: 1: In doTryCatch(return(expr), name, parentenv, handler) :   restarting interrupted promise evaluation 2: In doTryCatch(return(expr), name, parentenv, handler) :   restarting interrupted promise evaluation 

Ideally I want to avoid these messages altogether rather than just muffle them, since I might also want to handle genuine warnings coming from expr.

Answer 1

You can also try this without silent=TRUE if you want each error message to show. In neither case will you get the message about promises:

foo <- function() stop("Foo error") bar <- function(x) {     try(eval.parent(substitute(x)), silent = TRUE)     x } bar(foo())