The Art of R Programming

What is going on here? The main point is thatedtdbgsends remote com-

mands to the Vim text editor. For instance, if you are running Vim with a

server name of 168 and you want the cursor in Vim to move to line 12, you

could type this into a terminal (shell) window:

vim --remote-send 12G --servername 168

The effect would be the same as if you had physically typed12Gat the

Vim window. Since12Gis the Vim command to move the cursor to line 12,

that’s what would occur. Consider this call:

paste("vim --remote-send ",cmd," --servername ",vimserver,sep="")

Here,cmdis the string"12G",vimserveris 168 , andpaste()concatenates all

the indicated strings. The argumentsep=""says to use the empty string as

separator in this concatenation—that is, no separation. Thus,paste()returns

the following:

vim --remote-send 12G --servername 168

Another core element in the operation ofedtdbgis that the program

has arranged, via a call to R’ssink()function, to record to the filedbgsink

most output from R’s debugger in your R window. (Theedtdbgutility works

in concert with that debugger.) That information includes the line num-

bers of your positions in your source file as you step through it using R’s

debugger.

The line position information in the debugger output looks like this:

debug at cities.r#16: {

So, there is code inedtdbgto determine the latest line indbgsinkthat

begins with “debug at.” That line is then placed, as a string, in a variable

nameddebugline. The following code then extracts the line number (16 in

the example) and the source filename/Vim buffer name (cities.rhere):

linenumstart <- regexpr("#",debugline) + 1

buffname <- substr(debugline,10,linenumstart-2)

colon <- regexpr(":",debugline)

linenum <- substr(debugline,linenumstart,colon-1)

The call toregexpr()determines where indebuglinethe # character is

located (character 18 in this example). Adding 1 to that gives the position of

the line number withindebugline.

258 Chapter 11