R: Examples for 'base::delayedAssign'

### ** Examples

msg <- "old"
delayedAssign("x", msg)
substitute(x) # shows only 'x', as it is in the global env.

msg

msg <- "new!"
x # new!

[1] "new!"

delayedAssign("x", {
    for(i in 1:3)
        cat("yippee!\n")
    10
})

x^2 #- yippee

yippee!
yippee!
yippee!

[1] 100

x^2 #- simple number

[1] 100

ne <- new.env()
delayedAssign("x", pi + 2, assign.env = ne)
## See the promise {without "forcing" (i.e. evaluating) it}:
substitute(x, ne) #  'pi + 2'

pi + 2

## Don't show: 
stopifnot(identical(substitute(x,ne), quote(pi + 2)))
## End(Don't show)

### Promises in an environment [for advanced users]:  ---------------------

e <- (function(x, y = 1, z) environment())(cos, "y", {cat(" HO!\n"); pi+2})
## How can we look at all promises in an env (w/o forcing them)?
gete <- function(e_) {
   ne <- names(e_)
   names(ne) <- ne
   lapply(lapply(ne, as.name),
          function(n) eval(substitute(substitute(X, e_), list(X=n))))
}
(exps <- gete(e))

$x
cos

$y
[1] "y"

$z
{
    cat(" HO!\n")
    pi + 2
}

sapply(exps, typeof)

          x           y           z 
   "symbol" "character"  "language"

(le <- as.list(e)) # evaluates ("force"s) the promises

HO!

$x
function (x)  .Primitive("cos")

$y
[1] "y"

$z
[1] 5.141593

stopifnot(identical(le, lapply(exps, eval))) # and another "Ho!"

HO!

Examples for 'base::delayedAssign'

Delay Evaluation and Promises