R: Low-level Tcl/Tk Interface

TclInterface {tcltk}

R Documentation

Low-level Tcl/Tk Interface

Description

These functions and variables provide the basic glue between R and the Tcl interpreter and Tk GUI toolkit. Tk windows may be represented via R objects. Tcl variables can be accessed via the pseudo-list tclvar.

Usage

.Tcl(...)
.Tcl.args(...)
.Tcl.callback(...)
.Tk.ID(win)
.Tk.newwin(ID)
.Tk.subwin(parent)
.TkWin
.TkRoot

tkdestroy(win)
is.tkwin(x)

tclvar$name
tclvar$name <- value

Arguments

win

a window structure

x

an object

ID

a window ID

Details

Many of these functions are not intended for general use but are used internally by the commands that create and manipulate Tk widgets and Tcl objects. At the lowest level .Tcl sends a command as a text string to the Tcl interpreter and returns the result as a text string.

.Tcl.args converts an R argument list of tag=value pairs to the Tcl -option value style, thus enabling a simple translation between the two languages. To send a value with no preceding option flag to Tcl, just use an untagged argument. In the rare case one needs an option with no subsequent value tag=NULL can be used. Most values are just converted to character mode and inserted in the command string, but window objects are passed using their ID string, and functions are passed via the result of .Tcl.callback. Tags are converted to option flags simply by prepending a -

.Tcl.callback converts R functions to Tcl command strings. The argument must be a function closure. The return value is something of the form { R_call 0x408b94d4 } in which the hexadecimal number is the memory address of the function. .Tcl.args takes special precautions to ensure that the function will exist at that address by assigning the function into the relevant window environment (see below).

Tk windows are represented as R environments, all of which are enclosed in the .TkWin environment. They contain initially just an ID variable identical to the Tk window name, a parent variable and a num.subwin variable (possibly inherited from .TkWin). If the window obtains subwindows and callbacks, they are added as variables to the environment. .TkRoot is the top window with ID "."; this window is not displayed in order to avoid ill effects of closing it via window manager controls. .Tk.ID extracts the ID of a window, .Tk.newwin creates a new window environment with a given ID and .Tk.subwin creates a new window which is a subwindow of a given parent window.

tkdestroy destroys a window and also removes the reference to a window from its parent.

is.tkwin can be used to test whether a given object is a window environment.

tclvar is used to access Tcl variables. The Tcl variable name is used as if it were a list element name in tclvar, but in reality tclvar is an object of class tclvar and $ and $<- have special methods for that class.

Note