On Oct 17, 2006, at 8:33 PM, Martin Morgan wrote:
>> delayMe <- function() {
> + if (failed) {
> + delayedAssign("x", delayMe(), assign.env=topenv())
> + stop("init me!")
> + } else foo
> + }
>>
>> failed <- TRUE
>> foo <- "is me"
>> delayedAssign("x", delayMe())
>> x
> Error in delayMe() : init me!
>> x
> Error in delayMe() : init me!
>> failed <- FALSE
>> x
> [1] "is me"
>
> ??
>
This works only because you assigned both x and the delayMe function
to the global environment. This won't work in any other case (and no,
I didn't want to use this in the global environment - you shouldn't
be trashing it anyway ;)).
Of course you can recursively re-install the promise, but that's
beside the point.
FWIW a general solution re-installing the promise could look like this:
local({ ae<-parent.env(environment()); d<-function() {print
(environment()); if(failed) { delayedAssign("x", d(), assign.env=ae);
stop("init me!") } else foo}; delayedAssign("x", d(),assign.env=ae)})
However in my particular case the whole point of using a promise is
that I'm dealing with a sealed environment (namespace) so you cannot
re-install delayedAssign again (it will fail because the binding is
locked). If the promise worked as I envision, re-installing
delayedAssign would be unnecessary, because the promise is already in
place and will stay there until the evaluation is successful.
Cheers,
Simon
> Simon Urbanek <[EMAIL PROTECTED]> writes:
>
>> 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
>> Error: recursive default argument reference
>>
>> ^^-- from now on x is completely unusable - it has no value (i.e.
>> cannot be passed to any function) and yet won't be evaluated again
>>
>>> failed<-FALSE
>>> x
>> Error: recursive default argument reference
>>> delayedAssign("x", if (failed) stop("you have to initialize me
>> first!") else foo)
>>> x
>> [1] "I'm foo"
>>
>> I'd expect something like
>>> failed<-TRUE
>>> x
>> Error: you have to initialize me first!
>>> x
>> Error: you have to initialize me first!
>>> failed<-FALSE
>>> x
>> [1] "I'm foo"
>>
>> Is there a way to achieve that? Intuitively I'd think that this is
>> the desired behavior, because currently the promise is sort of
>> 'broken' after an error (AFAICT the behavior is not documented
>> anywhere) - but then, I wasn't messing with promises until now...
>>
>> Thanks,
>> Simon
>>
>> ______________________________________________
>> R-devel@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> --
> Martin T. Morgan
> Bioconductor / Computational Biology
> http://bioconductor.org
>
>
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