On Sat, 11 May 2024, Travers Ching wrote:
The following code snippet causes R to hang. This example might be a
bit contrived as I was experimenting and trying to understand
promises, but uses only base R.
It looks like it is looking for "not_a_variable" recursively but since
it doesn't exist it goes on indefinitely.
x0 <- new.env()
x1 <- new.env(parent = x0)
parent.env(x0) <- x1
delayedAssign("v", not_a_variable, eval.env=x1)
delayedAssign("w", v, assign.env=x1, eval.env=x0)
x1$w
This has nothing to do with promises. You created a cycle in the
environment chain. A simpler variant:
e <- new.env()
parent.env(e) <- e
get("x", e)
This will hang and is not interruptable -- loops searching up
environment chains are too speed-critical to check for interrupts. It
is, however, pretty easy to check whether the parent change would
create a cycle and throw an error if it would. Need to think a bit
about exactly where the check should go.
Best,
luke
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Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke-tier...@uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu/
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