R help - Aug 2013 - A question about using delayedAssign

I run the examples in delayedAssign:

msg <- "old"
delayedAssign("x", msg)
msg <- "new!"
x

If I run these four commands together, x is "new". If I run the first
two
commands first and then run the last two commands, x is "old".

I just cannot figure out why.

Thanks.
Gang

	[[alternative HTML version deleted]]

On 13-08-14 9:11 PM, Gang Peng wrote:
> I run the examples in delayedAssign:
>
> msg <- "old"
> delayedAssign("x", msg)
> msg <- "new!"
> x
>
> If I run these four commands together, x is "new". If I run the
first two
> commands first and then run the last two commands, x is "old".
>
> I just cannot figure out why.
You aren't telling us everything.  What did you do in between running 
the first two and the last two?  Presumably something you did forced the 
evaluation of x.  That is what causes the behaviour you saw.

Duncan Murdoch

Change
   delayedAssign("x", msg)
to
   delayedAssign("x", { cat("Assigning 'msg' to
'x' now\n") ; msg })
and you will see the message when the delayed assignment is triggered.
You could add print(sys.calls()) to that to see the call stack if it isn't
obvious.
> msg <- "old"
> delayedAssign("x", { cat("Assigning 'msg' to
'x' now\n") ; print(sys.calls()) ; msg })
> f <- function(p) paste(x, p)
> f("qwerty")
Assigning 'msg' to 'x' now
[[1]]
f("qwerty")

[[2]]
paste(x, p)

[[3]]
print(sys.calls())

[1] "old qwerty"
> x
[1] "old"


Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org] On Behalf
> Of Gang Peng
> Sent: Wednesday, August 14, 2013 6:12 PM
> To: r-help at r-project.org
> Subject: [R] A question about using delayedAssign
> 
> I run the examples in delayedAssign:
> 
> msg <- "old"
> delayedAssign("x", msg)
> msg <- "new!"
> x
> 
> If I run these four commands together, x is "new". If I run the
first two
> commands first and then run the last two commands, x is "old".
> 
> I just cannot figure out why.
> 
> Thanks.
> Gang
> 
> 	[[alternative HTML version deleted]]
> 
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