Show what's in .Internal function

internal.R

library("httr")
library("rjson")

internal <- function(fun){
  names.c <- content( GET("https://raw2.github.com/wch/r-source/trunk/src/main/names.c") )
  names.c <- strsplit( names.c, "\\n" )[[1L]]
  
  rx <- sprintf('^[{]"%s"', fun )
  match <- grep( rx, names.c)
  if( length(match) != 1L ){
    stop( "did not find a single match" )   
  }
  
  data <- strsplit( names.c[match], "[[:space:]]*,\\t[[:space:]]*" )[[1L]]
  
  impl <- data[2]
  url <- sprintf( 'https://github.com/search?q="SEXP attribute_hidden %s"+repo:wch/r-source&type=Code', impl)
  BROWSE(url)
}

# example use
internal( "is.vector" )

Sure. This has not been thoroughly tested though.

Just for the record if anybody comes back here. pryr now has this:
https://github.com/hadley/pryr/blob/master/R/names_c.R