如何找到 function 的源代码？

Question

我正在寻找 function 的源代码（从 package 'recurse' 获取递归），看看它是如何工作的。 这里，是我做的步骤：

getRecursions
function (x, radius, threshold = 0, timeunits = c("hours", 
    "secs", "mins", "days"), verbose = TRUE) 
{
    UseMethod("getRecursions", x)
}
<bytecode: 0x00000246a5983b30>
<environment: namespace:recurse>

methods(getRecursions)
[1] getRecursions.data.frame* getRecursions.Move*      
[3] getRecursions.MoveStack* 
see '?methods' for accessing help and source code

getAnywhere('getRecursions.data.frame')
A single object matching ‘getRecursions.data.frame’ was found
It was found in the following places
  registered S3 method for getRecursions from namespace recurse
  namespace:recurse
with value

function (x, radius, threshold = 0, timeunits = c("hours", 
    "secs", "mins", "days"), verbose = TRUE) 
{
    stopifnot(is.data.frame(x))
    stopifnot(ncol(x) == 4)
    stopifnot(radius > 0)
    timeunits = match.arg(timeunits)
    results = getRecursionsCpp(x[, 1], x[, 2], x[, 3], x[, 4], 
        x[, 1], x[, 2], radius, threshold, timeunits, verbose)
    results$timeunits = timeunits
    class(results) = "recurse"
    if (verbose) {
        class(results) = c("recurse", "recurse.verbose")
        dataTz = attr(x[, 3], "tzone")
        if (!is.null(dataTz)) {
            attr(results$revisitStats$entranceTime, "tzone") = dataTz
            attr(results$revisitStats$exitTime, "tzone") = dataTz
        }
    }
    return(results)
}
<bytecode: 0x00000247245c34c8>
<environment: namespace:recurse>

所以，现在我需要找到 function 'getRecursionsCpp' 的源代码，如下所示：

getAnywhere('getRecursionsCpp')
A single object matching ‘getRecursionsCpp’ was found
It was found in the following places
  namespace:recurse
with value

function (trajX, trajY, trajT, trajId, locX, locY, radius, threshold, 
    timeunits, verbose) 
{
    .Call("_recurse_getRecursionsCpp", PACKAGE = "recurse", 
        trajX, trajY, trajT, trajId, locX, locY, radius, threshold, 
        timeunits, verbose)
}
<bytecode: 0x0000024745a6ea20>
<environment: namespace:recurse>

如何找到 function call.Call("_recurse_getRecursionsCpp") 的源代码？ 我尝试使用这个recurse:::"_recurse_getRecursionsCpp" ，但它不起作用。