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 objects of class `tclVar` and the C level interface to Tcl objects is accessed via objects of class `tclObj`.

### Usage

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

    tkdestroy(win)
    is.tkwin(x)

    tclvalue(x)
    tclvalue(x) <- value

    tclVar(init = "")
    ## S3 method for class 'tclVar'
    as.character(x, ...)
    ## S3 method for class 'tclVar'
    tclvalue(x)
    ## S3 replacement method for class 'tclVar'
    tclvalue(x) <- value

    tclArray()
    ## S3 method for class 'tclArray'
    x[[...]]
    ## S3 replacement method for class 'tclArray'
    x[[...]] <- value
    ## S3 method for class 'tclArray'
    x$i
    ## S3 replacement method for class 'tclArray'
    x$i <- value

    ## S3 method for class 'tclArray'
    names(x)
    ## S3 method for class 'tclArray'
    length(x)

    tclObj(x)
    tclObj(x) <- value
    ## S3 method for class 'tclVar'
    tclObj(x)
    ## S3 replacement method for class 'tclVar'
    tclObj(x) <- value

    as.tclObj(x, drop = FALSE)
    is.tclObj(x)

    ## S3 method for class 'tclObj'
    as.character(x, ...)
    ## S3 method for class 'tclObj'
    as.integer(x, ...)
    ## S3 method for class 'tclObj'
    as.double(x, ...)
    ## S3 method for class 'tclObj'
    as.logical(x, ...)
    ## S3 method for class 'tclObj'
    as.raw(x, ...)
    ## S3 method for class 'tclObj'
    tclvalue(x)

    ## Default S3 method:
    tclvalue(x)
    ## Default S3 replacement method:
    tclvalue(x) <- value

    addTclPath(path = ".")
    tclRequire(package, warn = TRUE)

### Arguments

`objv` | a named vector of Tcl objects
`win` | a window structure
`x` | an object
`i` | character or (unquoted) name
`drop` | logical. Indicates whether a single-element vector should be made into a simple Tcl object or a list of length one
`value` | For `tclvalue` assignments, a character string. For `tclObj` assignments, an object of class `tclObj`
`ID` | a window ID
`parent` | a window which becomes the parent of the resulting window
`path` | path to a directory containing Tcl packages
`package` | a Tcl package name
`warn` | logical. Warn if not found?
`...` | Additional arguments. See below.
`init` | initialization value

### 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 an object of class `tclObj` (see below). A newer variant `.Tcl.objv` accepts arguments in the form of a named list of `tclObj` objects.

`.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 callbacks are passed via the result of `.Tcl.callback`. Tags are converted to option flags simply by prepending a `-`

`.Tcl.args.objv` serves a similar purpose as `.Tcl.args` but produces a list of `tclObj` objects suitable for passing to `.Tcl.objv`. The names of the list are converted to Tcl option style internally by `.Tcl.objv`.

Callbacks can be either atomic callbacks handled by `.Tcl.callback` or expressions. An expression is treated as a list of atomic callbacks, with the following exceptions: if an element is a name, it is first evaluated in the callers frame, and likewise if it is an explicit function definition; the `break` expression is translated directly to the Tcl counterpart. `.Tcl.callback` converts R functions and unevaluated calls to Tcl command strings. The argument must be either a function closure or an object of mode `"call"` followed by an environment. The return value in the first case is of the form `R_call 0x408b94d4` in which the hexadecimal number is the memory address of the function. In the second case it will be of the form `R_call_lang 0x8a95904 0x819bfd0`. For expressions, a sequence of similar items is generated, separated by semicolons. `.Tcl.args` takes special precautions to ensure that functions or calls will continue to exist at the specified address by assigning the callback into the relevant window environment (see below).

Tk windows are represented as objects of class `tkwin` which are lists containing a `ID` field and an `env` field which is an R environments, enclosed in the global environment. The value of the `ID` field is identical to the Tk window name. The `env` environment contains a `parent` variable and a `num.subwin` variable. If the window obtains sub-windows 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. The `parent` variable is undefined for `.TkRoot`.

`.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 sub-window 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` creates a new Tcl variable and initializes it to `init`. An R object of class `tclVar` is created to represent it. Using `as.character` on the object returns the Tcl variable name. Accessing the Tcl variable from R is done using the `tclvalue` function, which can also occur on the left-hand side of assignments. If `tclvalue` is passed an argument which is not a `tclVar` object, then it will assume that it is a character string explicitly naming global Tcl variable. Tcl variables created by `tclVar` are uniquely named and automatically unset by the garbage collector when the representing object is no longer in use.

`tclArray` creates a new Tcl array and initializes it to the empty array. An R object of class `tclArray` and inheriting from class `tclVar` is created to represent it. You can access elements of the Tcl array using indexing with `[[` or `$`, which also allow replacement forms. Notice that Tcl arrays are associative by nature and hence unordered; indexing with a numeric index `i` refers to the element with the name `as.character(i)`. Multiple indices are pasted together separated by commas to form a single name. You can query the length and the set of names in an array using methods for `length` and `names`, respectively; these cannot meaningfully be set so assignment forms exist only to print an error message.

It is possible to access Tcl's ‘dual-ported’ objects directly, thus avoiding parsing and deparsing of their string representation. This works by using objects of class `tclObj`. The string representation of such objects can be extracted (but not set) using `tclvalue` and conversion to vectors of mode `"character"`, `"double"`, `"integer"`, `"logical"`, and `"raw"` is performed using the standard coercion functions `as.character`, etc. Conversely, such vectors can be converted using `as.tclObj`. There is an ambiguity as to what should happen for length one vectors, controlled by the `drop` argument; there are cases where the distinction matters to Tcl, although mostly it treats them equivalently. Notice that `tclvalue` and `as.character` differ on an object whose string representation has embedded spaces, the former is sometimes to be preferred, in particular when applied to the result of `tclread`, `tkgetOpenFile`, and similar functions. The `as.raw` method returns a raw vector or a list of raw vectors and can be used to return binary data from Tcl.

The object behind a `tclVar` object is extracted using `tclObj(x)` which also allows an assignment form, in which the right hand side of the assignment is automatically converted using `as.tclObj`. There is a print method for `tclObj` objects; it prints `<Tcl>` followed by the string representation of the object. Notice that `as.character` on a `tclVar` object is the name of the corresponding Tcl variable and not the value.

Tcl packages can be loaded with `tclRequire`; it may be necessary to add the directory where they are found to the Tcl search path with `addTclPath`. The return value is a class `"tclObj"` object if it succeeds, or `FALSE` if it fails (when a warning is issued). To see the current search path as an R character vector, use

    strsplit(tclvalue('auto_path'), " ")[[1]]

.

### Note

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

### See Also

`TkWidgets`, `TkCommands`, `TkWidgetcmds`.

`capabilities("tcltk")` to see if Tcl/Tk support was compiled into this build of R.

### Examples

    ## Not run:
    ## 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()cat("HI!\n")
    .Tcl.callback(f)
    .Tcl.args(text = "Push!", command = f) # NB: Different address

    xyzzy <- tclVar(7913)
    tclvalue(xyzzy)
    tclvalue(xyzzy) <- "foo"
    as.character(xyzzy)
    tcl("set", as.character(xyzzy))

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

    ## End(Not run)

[Package tcltk version 3.1.2 Index]