[R] 'require' equivalent for local functions

[Duncan Murdoch]

On 22/03/2009 5:05 PM, JiHO wrote:
> Hello everyone,
> 
> I often create some local "libraries" of functions (.R files with only  
> functions in them) that I latter call. In scripts that call a function  
> from such library, I would like to be able to test whether the  
> function is already known in the namespace and, only if it is not,  
> source the library file. I.e. what `require` does for packages, I want  
> to do with my local functions.

That's pretty hard to make bulletproof.  Why not just put those 
functions in a package, and use that package?  If the functions are all 
written in R, creating the package is very easy:  see package.skeleton. 
  (And if you have a perfect memory and don't plan to distribute the 
package to anyone, you can skip documenting the functions:  then it's 
almost no work at all.)

Duncan Murdoch

> 
> Example:
> lib.R
> 	foo <- function(x) { x*2 }
> 
> script.R
> 	require.local(foo,"lib.R")
> 	# that searches for function "foo" and, if not found, executes  
> source("lib.R")
> 	foo(2)
> 
> Obviously, I want the test to be quite efficient otherwise I might as  
> well source the local library every time. I am aware that it would  
> probably not be able to check for changes in lib.R (i.e. do  
> complicated things such as re-source lib.R if foo in the namespace and  
> foo in lib.R are different), but that I can handle manually.
> 
> This seems like a common enough workflow but I cannot find a pre- 
> existing solution. Does anyone have pointers?
> 
> Otherwise I tried to put that together:
> 
> require.local <- function(fun, lib)
> #
> #	Searches for function "fun" and sources "lib" in
> #	case it is not found
> #
> {
> 	if (! (deparse(substitute(fun)) %in% ls(".GlobalEnv") && class(fun)  
> == "function") ) {
> 		cat("Sourcing", lib,"...\n")
> 		source(lib)
> 	}
> }
> 
> but I am really not confident with all those deparse/substitute things  
> and the environment manipulation, so I guess there should be a better  
> way.
> 
> JiHO
> ---
> http://jo.irisson.free.fr/
> 
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