Re: [Rd] Bug in handling of promises?
The following note in ?force may help
Note:
'force' does not force the evaluation of promises.
It is there because people have been confused before.
On Tue, 8 Mar 2005, Duncan Murdoch wrote:
I'm working on a function that does adaptive sampling, and I thought
it would be handy to return the function's environment as part of the
result so that I could re-use local variables in a subsequent run. My
first try didn't work, and it came down to code like this:
f - function( H, prevEnv = NULL) {
+ if (!is.null(prevEnv)) H - prevEnv$H
+ cat('Evaluate H to get ', H(1), '\n')
+ return(environment(NULL))
+ }
I thought that evaluating H would force it, so that H would be
available in the environment returned by the function. But this is
not so:
env - f( function(x) x^2 )
Evaluate H to get 1
env$H
promise: 012094D8
env$H(1)
Error: attempt to apply non-function
So I tried to explicitly force it:
g - function( H, prevEnv = NULL) {
+ if (!is.null(prevEnv)) H - prevEnv$H
+ force(H)
+ return(environment(NULL))
+ }
but this still doesn't work:
env - g( function(x) x^2 )
env$H
promise: 01206FC0
env$H(1)
Error: attempt to apply non-function
It seems that I need to do an assignment to convert H from a promise
to an evaluated object:
h - function( H, prevEnv = NULL) {
+ if (!is.null(prevEnv)) H - prevEnv$H
+ H - H
+ return(environment(NULL))
+ }
env - h( function(x) x^2 )
env$H
function(x) x^2
env$H(1)
[1] 1
Is this a bug, or just the way things are?
I get the same results in both R-patched and R-devel.
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UKFax: +44 1865 272595
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Re: [Rd] Bug in handling of promises?
On Tue, 8 Mar 2005 17:44:41 + (GMT), Prof Brian Ripley
[EMAIL PROTECTED] wrote :
The following note in ?force may help
Note:
'force' does not force the evaluation of promises.
It is there because people have been confused before.
Yes, but it also says that it forces the evaluation of a function
argument, which is what I was trying to do.
But mainly what may be a bug is the fact that H was available in env
but its value was not, even though it had already been evaluated in
that environment.
My examples were unnecessarily complicated last time, because they
were too much like the original. Here are simpler versions:
f - function( H ) {
+ cat('Evaluate H to get ', H, '\n')
+ return(environment())
+ }
env - f( 1 )
Evaluate H to get 1
env$H
promise: 0118BF1C
g - function( H ) {
+ force(H)
+ return(environment())
+ }
env - g( 2 )
env$H
promise: 0118A148
h - function( H ) {
+ H - H
+ return(environment())
+ }
env - h( 3 )
env$H
[1] 3
Duncan Murdoch
On Tue, 8 Mar 2005, Duncan Murdoch wrote:
I'm working on a function that does adaptive sampling, and I thought
it would be handy to return the function's environment as part of the
result so that I could re-use local variables in a subsequent run. My
first try didn't work, and it came down to code like this:
f - function( H, prevEnv = NULL) {
+ if (!is.null(prevEnv)) H - prevEnv$H
+ cat('Evaluate H to get ', H(1), '\n')
+ return(environment(NULL))
+ }
I thought that evaluating H would force it, so that H would be
available in the environment returned by the function. But this is
not so:
env - f( function(x) x^2 )
Evaluate H to get 1
env$H
promise: 012094D8
env$H(1)
Error: attempt to apply non-function
So I tried to explicitly force it:
g - function( H, prevEnv = NULL) {
+ if (!is.null(prevEnv)) H - prevEnv$H
+ force(H)
+ return(environment(NULL))
+ }
but this still doesn't work:
env - g( function(x) x^2 )
env$H
promise: 01206FC0
env$H(1)
Error: attempt to apply non-function
It seems that I need to do an assignment to convert H from a promise
to an evaluated object:
h - function( H, prevEnv = NULL) {
+ if (!is.null(prevEnv)) H - prevEnv$H
+ H - H
+ return(environment(NULL))
+ }
env - h( function(x) x^2 )
env$H
function(x) x^2
env$H(1)
[1] 1
Is this a bug, or just the way things are?
I get the same results in both R-patched and R-devel.
__
R-devel@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] Bug in handling of promises?
A followup: doing an assignment of the value works even after the
return:
f
function( H ) {
cat('Evaluate H to get \n')
print(H)
return(environment())
}
env - f( function(x) x^2 )
Evaluate H to get
function(x) x^2
env$H
promise: 0117C2D0
env$H(1)
Error: attempt to apply non-function
H - env$H
H(1)
[1] 1
So the oddity is that I can evaluate H within f() without any problem,
but outside of f() I need extra work before I can do it.
Duncan Murdoch
On Tue, 08 Mar 2005 18:00:10 +, Duncan Murdoch
[EMAIL PROTECTED] wrote :
On Tue, 8 Mar 2005 17:44:41 + (GMT), Prof Brian Ripley
[EMAIL PROTECTED] wrote :
The following note in ?force may help
Note:
'force' does not force the evaluation of promises.
It is there because people have been confused before.
Yes, but it also says that it forces the evaluation of a function
argument, which is what I was trying to do.
But mainly what may be a bug is the fact that H was available in env
but its value was not, even though it had already been evaluated in
that environment.
My examples were unnecessarily complicated last time, because they
were too much like the original. Here are simpler versions:
f - function( H ) {
+ cat('Evaluate H to get ', H, '\n')
+ return(environment())
+ }
env - f( 1 )
Evaluate H to get 1
env$H
promise: 0118BF1C
g - function( H ) {
+ force(H)
+ return(environment())
+ }
env - g( 2 )
env$H
promise: 0118A148
h - function( H ) {
+ H - H
+ return(environment())
+ }
env - h( 3 )
env$H
[1] 3
Duncan Murdoch
On Tue, 8 Mar 2005, Duncan Murdoch wrote:
I'm working on a function that does adaptive sampling, and I thought
it would be handy to return the function's environment as part of the
result so that I could re-use local variables in a subsequent run. My
first try didn't work, and it came down to code like this:
f - function( H, prevEnv = NULL) {
+ if (!is.null(prevEnv)) H - prevEnv$H
+ cat('Evaluate H to get ', H(1), '\n')
+ return(environment(NULL))
+ }
I thought that evaluating H would force it, so that H would be
available in the environment returned by the function. But this is
not so:
env - f( function(x) x^2 )
Evaluate H to get 1
env$H
promise: 012094D8
env$H(1)
Error: attempt to apply non-function
So I tried to explicitly force it:
g - function( H, prevEnv = NULL) {
+ if (!is.null(prevEnv)) H - prevEnv$H
+ force(H)
+ return(environment(NULL))
+ }
but this still doesn't work:
env - g( function(x) x^2 )
env$H
promise: 01206FC0
env$H(1)
Error: attempt to apply non-function
It seems that I need to do an assignment to convert H from a promise
to an evaluated object:
h - function( H, prevEnv = NULL) {
+ if (!is.null(prevEnv)) H - prevEnv$H
+ H - H
+ return(environment(NULL))
+ }
env - h( function(x) x^2 )
env$H
function(x) x^2
env$H(1)
[1] 1
Is this a bug, or just the way things are?
I get the same results in both R-patched and R-devel.
__
R-devel@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
__
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