similar to: Variable alias

After a bunch of discussion in the core group, we have decided to deprecate the delay() function (which was introduced as "experimental" in R 0.50). This is the function that duplicates in R code the delayed evaluation mechanism (the promise) that's used in evaluating function arguments. The problem with delay() was that it was handled inconsistently (e.g. sometimes you would see

Hi, I am looking for a way to find out the last expression that was entered by the user, similar to ".Last.value", but for the unevaluated expression instead of the evaluated one. Example: > x <- 4 > x*x + 3 [1] 19 > .Last.value # that's the evaluated last expression [1] 19 # but I am looking for the unevaluated expression (".Last.expression", so to

Hi all, The documentation for substitute currently reads: Substitution takes place by examining each component of the parse tree as follows: If it is not a bound symbol in ?env?, it is unchanged. If it is a promise object, i.e., a formal argument to a function or explicitly created using ?delayedAssign()?, the expression slot of the promise replaces the symbol. If it is an ordinary variable,

I noticed something recently that I thought was odd: delayedAssign("x", { Sys.sleep(5); 1 }) x ## Hit Ctrl-C within the first second or 2 gives me: > delayedAssign("x", { Sys.sleep(5); 1 }) > x ## Hit Ctrl-C within the first second or two > x Error: recursive default argument reference > My only problem here is that now I'm stuck---there's no way

Hello, ?delayedAssign presents substitute() as a way to look at the expression in the promise. However, msg <- "old" delayedAssign("x", msg) msg <- "new!" x #- new! substitute(x) #- x (was 'msg' ?) Here, we just got 'x'... shouldn't we got 'msg'? Same result when the promise is not evaluated yet: delayedAssign("x",

On Mon, Jan 26, 2015 at 12:24 PM, Hadley Wickham <h.wickham at gmail.com> wrote: > If it was any other environment than the global, you could use substitute: > > e <- new.env() > delayedAssign("foo", stop("Hey!"), assign.env = e) > substitute(foo, e) > > delayedAssign("foo", stop("Hey!")) > substitute(foo) Hmm... interesting

Duncan, Thank you for the clarification on how delayedAssign works. Should R-level interfaces to promise objects ever become available, I expect they would at time come in handy. On the subject of substitute and delayedAssign, I do have a follow-up question for the list. I'm trying to convert a named list of expression objects into an environment of promise objects. After conversion, each

I'm not sure if this is a known peculiarity or a bug, but I stumbled across what I think is very odd behavior from delayedAssign. In the below example x switches values the first two times it is evaluated. > delayedAssign("x", {x <- 2; x+3}) > x==x [1] FALSE > delayedAssign("x", {x <- 2; x+3}) > x [1] 5 > x [1] 2 The ?delayedAssign documentation says

Hi, I wanted a Q&D way to open a new graphics window but keep the focus in the console window (under Windows and the Rgui), so I wrote a line into my Rprofile.site file as follows: invisible(makeActiveBinding('newdev', function(...) dev.new(restoreConsole=T), .GlobalEnv)) (That is all on one line, incase the mailer re-parses it). This gives me a command "newdev" which

Hi all, The help for delayedAssign suggests that you can use substitute to access the expression associated with a promise, and the help for substitute says: "If it is a promise object, i.e., a formal argument to a function or explicitly created using ?delayedAssign()?, the expression slot of the promise replaces the symbol. But this doesn't seem to work: > a <- 1 > b <- 2

The last two lines of example(delayedAssign) give this: > e <- (function(x, y = 1, z) environment())(1+2, "y", {cat(" HO! "); pi+2}) > (le <- as.list(e)) # evaluates the promises $x <promise: 0x032b31f8> $y <promise: 0x032b3230> $z <promise: 0x032b3268> which contrary to the comment appears unevaluated. Is the comment wrong or is it supposed to

The help files for delayedAssign and substitute both say that substitute() can be used to see the expression associated with a promise. However, I can't see how to do that. When I try the example in help file for delayedAssign I don't see substitute() extracting the promise, e.g.: > msg <- "old" > delayedAssign("x", msg) > msg <-

Hi, I got an interesting programming challenge: How do you inspect an object which is assigned via delayedAssign() and that throws an error as soon as it is "touched" (=the value is evaluated)? Is it possible? MINIMAL EXAMPLE: $ R --vanilla > delayedAssign("foo", stop("Hey!")) (If you find this minimal example silly/obvious, please skip down to the real

Is there a way to raise an error condition when a promise is evaluated such that is can be evaluated again? Right now strange things happen when the evaluation fails: > delayedAssign("x", if (failed) stop("you have to initialize me first!") else foo) > foo <- "I'm foo" > failed<-TRUE > x Error: you have to initialize me first! > x

Hello, Are there any recipe to handle serialization / deserialization of external pointers. I'm thinking about something similar in spirit to the way we handle finalization of external pointers. Currently, if we create an external pointer, save the session, quit R, then load the session, we get a null pointer. One way I'm thinking of is to have an environment in the

Hi, I stumbled upon a surprising behavior when using an active binding as a loop index variable in R 4.0.0. In contrast, the behavior observed in R 3.6.1 is in line with my expectations. Consider the code below: makeActiveBinding("i", function(value) { if (missing(value)) { x } else { print("set") x <<- value } }, globalenv()) i <- 1 # output

Hi, The problem arises when I lazyLoad() the .Random.seed from a previously saved database. To simplify the process of reproducing the problem, see the example below: ## this assignment may not really make sense, but illustrates the problem delayedAssign('.Random.seed', 1L) typeof(.Random.seed) # [1] "integer" rnorm(1) # Error in rnorm(1) : # .Random.seed is not an integer

Hi, The problem arises when I lazyLoad() the .Random.seed from a previously saved database. To simplify the process of reproducing the problem, see the example below: ## this assignment may not really make sense, but illustrates the problem delayedAssign('.Random.seed', 1L) typeof(.Random.seed) # [1] "integer" rnorm(1) # Error in rnorm(1) : # .Random.seed is not an integer

R-devel, I used the 'substitute' function to create labels for objects inside an environment, without actually evaluating the objects, as the objects might be promises. However, I was surprised to see that 'substitute' returns the expression slot of the original promise even after the promise has been forcibly evaluated. (Doesn't the promise go away after evaluation?) This

Is there some way of displaying the expression and evaluation environment associated with a promise? I have found the following: > # first run these two commands to set up example > e <- new.env() > delayedAssign("y", x*x, assign.env = e) > # method 1. shows expression but not evaluation environment > str(as.list(e)) List of 1 $ y: promise to language x * x >