R help - Apr 2009 - Using trace

I would like to trace functions, displaying their arguments and return
value, but I haven't been able to figure out how to do this with the
'trace' function.

After some thrashing, I got as far as this:

    fact <- function(x) if(x<1) 1 else x*fact(x-1)
    tracefnc <- function() dput(as.list(parent.frame()),  #
parent.frame() holds arg list
                                                control=NULL)
    trace("fact",tracer=tracefnc,print=FALSE)

but I couldn't figure out how to access the return value of the
function in the 'exit' parameter.  The above also doesn't work for
"..." arguments.  (More subtly, it forces the evaluation of promises
even if they are otherwise unused -- but that is, I suppose, a weird
and obscure case.)

Surely someone has solved this already?

What I'm looking for is something very simple, along the lines of
old-fashioned Lisp trace:
> defun fact (i) (if (< i 1) 1 (* i (fact (+ i -1)))))
FACT
> (trace fact)
(FACT)
> (fact 3)
  1> (FACT 3)
    2> (FACT 2)
      3> (FACT 1)
        4> (FACT 0)
        <4 (FACT 1)
      <3 (FACT 1)
    <2 (FACT 2)
  <1 (FACT 6)
6

Can someone help? Thanks,

         -s

I posted the query below on r-help, but perhaps r-devel is more
suitable... (I guess "r-devel" should be read as "those who
develop
(i.e. write) programs in R" rather than "those who develop R"?)

             -s

I would like to trace functions, displaying their arguments and return
value, but I haven't been able to figure out how to do this with the
'trace' function.

After some thrashing, I got as far as this:

? ?fact <- function(x) if(x<1) 1 else x*fact(x-1)
? ?tracefnc <- function() dput(as.list(parent.frame()), ?#
parent.frame() holds arg list
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?control=NULL)
? ?trace("fact",tracer=tracefnc,print=FALSE)

but I couldn't figure out how to access the return value of the
function in the 'exit' parameter. ?The above also doesn't work for
"..." arguments. ?(More subtly, it forces the evaluation of promises
even if they are otherwise unused -- but that is, I suppose, a weird
and obscure case.)

Surely someone has solved this already?

What I'm looking for is something very simple, along the lines of
old-fashioned Lisp trace:
> defun fact (i) (if (< i 1) 1 (* i (fact (+ i -1)))))
FACT
> (trace fact)
(FACT)
> (fact 3)
?1> (FACT 3)
? ?2> (FACT 2)
? ? ?3> (FACT 1)
? ? ? ?4> (FACT 0)
? ? ? ?<4 (FACT 1)
? ? ?<3 (FACT 1)
? ?<2 (FACT 2)
?<1 (FACT 6)
6

Can someone help? Thanks,

? ? ? ? -s

Can you just print what you need to know? For example:
> fact <- function(x) {
+ if(x<1) ans <- 1 else ans <- x*fact(x-1)
+ print(sys.call())
+ cat(sprintf("X is %i\n",x))
+ print(ans)
+ }
> fact(4)
fact(x - 1)
X is 0
[1] 1
fact(x - 1)
X is 1
[1] 1
fact(x - 1)
X is 2
[1] 2
fact(x - 1)
X is 3
[1] 6
fact(4)
X is 4
[1] 24


2009/4/13 Stavros Macrakis <macrakis at
alum.mit.edu>:
> I would like to trace functions, displaying their arguments and return
> value, but I haven't been able to figure out how to do this with the
> 'trace' function.
>
> After some thrashing, I got as far as this:
>
> ? ?fact <- function(x) if(x<1) 1 else x*fact(x-1)
> ? ?tracefnc <- function() dput(as.list(parent.frame()), ?#
> parent.frame() holds arg list
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?control=NULL)
> ? ?trace("fact",tracer=tracefnc,print=FALSE)
>
> but I couldn't figure out how to access the return value of the
> function in the 'exit' parameter. ?The above also doesn't work
for
> "..." arguments. ?(More subtly, it forces the evaluation of
promises
> even if they are otherwise unused -- but that is, I suppose, a weird
> and obscure case.)
>
> Surely someone has solved this already?
>
> What I'm looking for is something very simple, along the lines of
> old-fashioned Lisp trace:
>
>> defun fact (i) (if (< i 1) 1 (* i (fact (+ i -1)))))
> FACT
>> (trace fact)
> (FACT)
>> (fact 3)
> ?1> (FACT 3)
> ? ?2> (FACT 2)
> ? ? ?3> (FACT 1)
> ? ? ? ?4> (FACT 0)
> ? ? ? ?<4 (FACT 1)
> ? ? ?<3 (FACT 1)
> ? ?<2 (FACT 2)
> ?<1 (FACT 6)
> 6
>
> Can someone help? Thanks,
>
> ? ? ? ? -s
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
HUANG Ronggui, Wincent
PhD Candidate
Dept of Public and Social Administration
City University of Hong Kong
Home page: http://asrr.r-forge.r-project.org/rghuang.html