mget call can trigger C stack usage error

Alexandre,

AFAICS, this code actually causes infinite recursion, and here's why:


   1. formals grabs returns the formals of the function identified by
   sys.function(sys.parent()) this ends up being print.new, whose first
   argument is x
   2. mget looks for the symbol x in envir = as.environment(-1L) which ends
   up being the evaluation frame for print.new [1]
   3. x in that environment resolves the the object you are trying to print
   4. print() is called on that object, and dispatches to print.new() ...



[1]

debug(mget)

foo

*<snip>*

[1] "envir"      "ifnotfound" "inherits"   "mode"       "x"

Browse[2]> *envir*

*<environment: 0x7fa39bf1b278>*

Browse[2]> sys.frames()

[[1]]

<environment: 0x7fa39bf1b550>


*[[2]]*

*<environment: 0x7fa39bf1b278>*


*<snip>*


Browse[2]> sys.calls()

[[1]]

function (x, ...)

UseMethod("print")(x)


*[[2]]*

*print.new(x)*


*<snip>*


Browse[2]> class(envir$x)

[1] *"new"*

Hope that helps.
~G

On Mon, Sep 5, 2016 at 4:48 PM, Alexandre Courtiol <

Hi all, not sure if you will call this a bug or something else but the
following silly call trigger a low level error:

foo <- list(x=1)
class(foo) <- "new"
print.new <- function(x, ...) print(mget(names(formals())))
foo

Error: C stack usage  7969412 is too close to the limit

--
Alexandre Courtiol

http://sites.google.com/site/alexandrecourtiol/home

*"Science is the belief in the ignorance of experts"*, R. Feynman

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