Please note that this is documented in ?trace. "fun" is matched to what, it is a _name_ of the function to be traced, which is traced in the top-level environment. I don't know why it was designed this way, but it is documented in detail, and hence the expected behavior.

Debugging is often, and also in R, implemented in the core. Tracing is implemented on top without specific support, it thus cannot do some things debugging can do.

Tomas


On 8/26/20 3:31 AM, Antoine Fabri wrote:
Apologies there is one line missing in my last email, the code should be :

foo <- function() "hello"
trace2 <- function(fun) trace(fun, quote(print("!!!")))
trace2(foo) # <- THIS LINE WAS MISSING
base::fun

Best,

Antoine

Le mar. 25 août 2020 à 22:02, Antoine Fabri <antoine.fa...@gmail.com> a
écrit :

Dear R-devel,

I don't think this is expected :

foo <- function() "hello"
trace2 <- function(fun) trace(fun, quote(print("!!!")))
base::fun
# Object with tracing code, class "functionWithTrace"
# Original definition:
# function() "hello"
#
# ## (to see the tracing code, look at body(object))

`untrace()` has the same behavior.

This is inconsistent with how debug works :

foo <- function() "hello"
debug2 <- function(fun) debug(fun)
debug2(foo)
isdebugged(foo)
# [1] TRUE

This can be worked around by defining :

trace2 <- function(fun) eval.parent(substitute(trace(fun,
quote(print("!!!")))

but I believe the current behavior is undesired and it'd be better to make
it behave as `debug()`, or to throw an error.

Best,

Antoine

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