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

Strings containing unbalanced braces are currently not handled well in many circumstances.

### Examples

    ## These cannot be run by example() but should be OK when pasted
    ## into an interactive R session with the tcltk package loaded
    .Tcl("format \"%s\n\" \"Hello, World!\"")
    f <- function()"HI!"
    .Tcl.callback(f)
    .Tcl.args(text="Push!", command=f) # NB: Different address

    tclvar$xyzzy <- 7913 ; .Tcl("set xyzzy")
    .Tcl("set xyzzy 3917") ; tclvar$xyzzy

    top <- tktoplevel() # a Tk widget, see Tk-widgets
    ls(envir=top, all=TRUE)
    ls(envir=.TkRoot, all=T)# .Tcl.args put a callback ref in here

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