Simple mechanism for attaching functions in a single .R file

tach.R

###
### tach (c) Barry Rowlingson, 2012, pronounced like "tash"
###
### tach("file.R") will source that file into an environment and
### put it on the search path, thus including any function
### definitions without polluting your GlobalEnv
###
### retach() will scan your search path for any tach'ed files and
### if they have been modified since they were loaded they'll be
### re-tached.
###
### To remove, just use detach(pos) where pos is the position
###

### until this makes it into a package (or oblivion) you can do:
###
###  source("tach.R");tach("tach.R");rm(tach,retach)
###
### and then you've tach'ed tach itself and cleaned up.
###
### TODO: check for multiple taching the same file
###       verbosity reporting
###       smarter detach
###       print method for fileenv
###       tach whole directories of .R files. But that's nearly a package.

tach <- function(file){
###
### source a file into an environment and attach
### to the search path
### 
  e = new.env()
  source(file,e)
  me = attach(e,name=sprintf("file:%s",file))
###
### superclass it and add some metadata
###
  class(me)=c("fileenv","environment")
  attr(me,"src")=normalizePath(file)
  attr(me,"loaded")=Sys.time()
}

retach <- function(){
### scan the search path for fileenv class objects
  s = search()
  for(pos in 1:length(s)){
    e = pos.to.env(pos)
    if(inherits(e,"fileenv")){
      ## look for modification since last source
      cat(s[pos]," is a file env\n")
      when = attr(e,"loaded")
      fmod = file.info(attr(e,"src"))$mtime
      if(when < fmod){
        ## re-source it, update timestamp
        cat(s[pos], " changed since load\n")
        remove(list = ls(e),envir=e)
        source(attr(e,"src"),e)
        attr(e,"loaded")=Sys.time()
      }
    }
  }
}