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functions as arguments to ther functions with inlinedocs

5 messages · Duncan Murdoch, Rui Barradas, Jannis

Original
Jannis
# 
Dear R community,

I have a problem when I use functions as default values for argumnents 
in other functions. When I use curly brackets { here, I can not create a 
package with inlinedocs. It will give me the error when using 
package.skeleton() in my package structure:

Error in parse(text = utxt) : <text>:4:0: unexpected end of input


For example:

dummyfunction = function(filters = function(x) {b = 0; x > b} ))
{
   # rest of code here
   return(filters)
}


This seems to me as a legal function declaration but creates the above 
mentioned error. Is this an error of inlinedocs or do I misunderstand 
the R language? Or is there another way of using functions in such a way 
as arguments? In this case I could easily define this filters argument 
inside the function for cases when it is not supplied as an argument but 
I have some more complex functions where I really need to define 
something sequential as an argument like:

dummyfunction = function(filters = {a = 1; b > a; b}) {print('test')}


I hope I could clarify my problem.


Thanks a lot
Jannis
Duncan Murdoch
#
On 24/01/2013 1:32 PM, Jannis wrote:
The definition above is not syntactically correct, it has an extra 
closing paren on the first line.  This would be correct:

dummyfunction = function(filters = function(x) {b = 0; x > b} )
{
    # rest of code here
    return(filters)
}

If that still confuses inlinedocs, then it's a bug in that package. This 
might be easier for it to handle:


dummyfunction = function(filters)
{
    if (missing(filters)) filters <- function(x) {b = 0; x > b}
    # rest of code here
    return(filters)
}


and it should be equivalent to the original.
That's a pretty strange definition.  I would have written it as

dummyfunction = function(filters = b) {
{   a = 1
     b > a
     b
     print('test')
}

Remember that defaults for function arguments are evaluated in the evaluation frame of the function, not
in the caller's evaluation frame, so they don't need to exist when you enter the function, only when you first use the associated argument.

Duncan Murdoch
Rui Barradas
# 
Hello,

Your function declaration has a syntax error, one left parenthesis too 
much. Corrected it would be


dummyfunction <- function(filters = function(x) {b = 0; x > b} ){
   # rest of code here
   filters  # this returns a function, don't need return()
}

x <- -5:5
f <- dummyfunction()  # this creates the default function
f(x)

g <- dummyfunction(mean)  # this creates another function
g(x)


As you can see, you can use default functions as arguments in your 
function declaration.


Hope this helps,

Rui Barradas

Em 24-01-2013 18:32, Jannis escreveu:
Rui Barradas
# 
Hello,

Sorry, it's RIGHT parenthesis.


Rui Barradas
Em 24-01-2013 18:54, Rui Barradas escreveu:
Jannis
# 
Dear Duncan, dear Rui,


thanks for your replies. You are correct regarding the additional 
paranthesis. I probably copied the wrong code. I, however, get this 
inlinedocs error with the correct version. After contacting the package 
maintainer I think this is now added to inlinedocs list of bugs.


Thanks agian for replies!
Jannis
On 24.01.2013 20:02, Rui Barradas wrote: