R help - Dec 2021 - How to modify object's code living in some environment?

On 27/12/2021 8:25 a.m., Duncan Murdoch wrote:
> On 27/12/2021 8:06 a.m., Grzegorz Smoli?ski wrote:
>> Hi,
>>
>> I know it is possible to find the environment in which some object
>> lives using the 'environment()' function and the name of this
object,
>> but how to modify code of this object after this? Below is MRE:
> 
> You are misunderstanding the relation between environments and
> functions.  However, your understanding is also being messed up by a bug
> in R, so it's not entirely your fault.
> 
> More details below:
>>
>> test <- function() 1
>>
>> test() # 1
>>
>> environment(test)$test <- eval(parse(text = "function()
2"))
> 
> First:  while it's usually true that function f will be found in
> environment(f), these are really separate concepts.
> 
> The environment of a function is where it will start looking for
> non-local variables. It is initially the environment in which the
> function definition is evaluated.
> 
> The environment holding a function can be completely different.  This
> most commonly shows up when you have functions that create other
> functions.  For example,
> 
>     factory <- function(x) {
>       force(x)
>       function() print(x)
>     }
> 
>     f <- factory(3)
>     f()
> 
> which will print 3.  Here environment(f) is the evaluation frame of the
> call to factory(3), while f is not stored there, it is stored in the
> global environment.  (If you run ls(environment(f)) you won't see
"f"
> listed, only "x".)
> 
> In your first line "test <- function() 1" you create a
function named
> test in the global environment whose environment is also the global
> environment.
> 
> The third line should do what you want, i.e. put the new definition into
> the environment of the test function, using the name test, but it
> doesn't:  I think that's a bug in R.  It should be equivalent to
> 
>     .GlobalEnv$test <- eval(parse(text = "function() 2"))
> 
> or
> 
>     test <- eval(parse(text = "function() 2"))
> 
> but as you saw, it's not.  They do what you were expecting your third
> line to do.
> 
>>
>> test() # still 1
>>
>> .GlobalEnv$test <- eval(parse(text = "function() 3"))
>>
>> test() # 3
>>
>> The context is I have shiny app which code I would like to modify (add
>> something) and the only way to refer to this environment I know is to
>> use 'environment()' (as I see, those functions do not live in
>> .GlobalEnv), but as you can see above, I can't use it to modify the
>> code.
> 
> You can, as long as you work around the bug in R.  Just change that
> third line into two statements:
> 
>     e <- environment(test)
>     e$test <- eval(parse(text = "function() 2"))
> 
And I forgot to mention, as Ivan did, that this might not do what you 
want, because of the difference in the concepts of "environment(f)"
and
"environment where f is found".

Duncan Murdoch

Thank you, Ivan and Duncan. The truth is I still feel lost in this
concept of environments, generally speaking.

What I really thought about is the possibility to make a shiny app
where there will be possible to choose the function name (from the set
of all functions defined in this app / modules / other helper files
sourced on the start of app) and write on the beginning of the body of
this chosen function 'browser()'. I have developed an app using
modules and I have found that it is not convenient to stop the app,
write 'browser()' where needed, start the app and make something to
run the function where is `browser()`, so I have started to think if I
could write this `browser()` on demand, using the app itself (so:
without stopping the app), then make something to run the function,
where is 'browser()' and enabling interactive debugger. But I see now
it is not good to make too many assumptions didn't knowing some topic
:)

pon., 27 gru 2021 o 14:27 Duncan Murdoch <murdoch.duncan at gmail.com>
napisa?(a):
>
> On 27/12/2021 8:25 a.m., Duncan Murdoch wrote:
> > On 27/12/2021 8:06 a.m., Grzegorz Smoli?ski wrote:
> >> Hi,
> >>
> >> I know it is possible to find the environment in which some object
> >> lives using the 'environment()' function and the name of
this object,
> >> but how to modify code of this object after this? Below is MRE:
> >
> > You are misunderstanding the relation between environments and
> > functions.  However, your understanding is also being messed up by a
bug
> > in R, so it's not entirely your fault.
> >
> > More details below:
> >>
> >> test <- function() 1
> >>
> >> test() # 1
> >>
> >> environment(test)$test <- eval(parse(text = "function()
2"))
> >
> > First:  while it's usually true that function f will be found in
> > environment(f), these are really separate concepts.
> >
> > The environment of a function is where it will start looking for
> > non-local variables. It is initially the environment in which the
> > function definition is evaluated.
> >
> > The environment holding a function can be completely different.  This
> > most commonly shows up when you have functions that create other
> > functions.  For example,
> >
> >     factory <- function(x) {
> >       force(x)
> >       function() print(x)
> >     }
> >
> >     f <- factory(3)
> >     f()
> >
> > which will print 3.  Here environment(f) is the evaluation frame of
the
> > call to factory(3), while f is not stored there, it is stored in the
> > global environment.  (If you run ls(environment(f)) you won't see
"f"
> > listed, only "x".)
> >
> > In your first line "test <- function() 1" you create a
function named
> > test in the global environment whose environment is also the global
> > environment.
> >
> > The third line should do what you want, i.e. put the new definition
into
> > the environment of the test function, using the name test, but it
> > doesn't:  I think that's a bug in R.  It should be equivalent
to
> >
> >     .GlobalEnv$test <- eval(parse(text = "function() 2"))
> >
> > or
> >
> >     test <- eval(parse(text = "function() 2"))
> >
> > but as you saw, it's not.  They do what you were expecting your
third
> > line to do.
> >
> >>
> >> test() # still 1
> >>
> >> .GlobalEnv$test <- eval(parse(text = "function() 3"))
> >>
> >> test() # 3
> >>
> >> The context is I have shiny app which code I would like to modify
(add
> >> something) and the only way to refer to this environment I know is
to
> >> use 'environment()' (as I see, those functions do not live
in
> >> .GlobalEnv), but as you can see above, I can't use it to
modify the
> >> code.
> >
> > You can, as long as you work around the bug in R.  Just change that
> > third line into two statements:
> >
> >     e <- environment(test)
> >     e$test <- eval(parse(text = "function() 2"))
> >
>
> And I forgot to mention, as Ivan did, that this might not do what you
> want, because of the difference in the concepts of
"environment(f)" and
> "environment where f is found".
>
> Duncan Murdoch