mvbutils (version 2.5.4)

mvb.sys.parent: Functions to Access the Function Call Stack

Description

These functions are "do what I mean, not what I say" equivalents of the corresponding system functions. The system functions can behave strangely when called in strange ways (primarily inside eval calls). The mvb equivalents behave in a more predictable fashion.

Usage

mvb.sys.parent(n=1)
mvb.sys.nframe()
mvb.parent.frame(n=1)
mvb.match.call(definition = sys.function(mvb.sys.parent()),
    call = sys.call(mvb.sys.parent()),  expand.dots = TRUE)
mvb.nargs()
mvb.sys.call(which = 0)
mvb.sys.function(n)
mvb.sys.on.exit()

Arguments

which

the frame number if non-negative, the number of generations to go back if negative. (See the Details section.)

n

the number of frame generations to go back.

definition

a function, by default the function from which match.call is called.

call

an unevaluated call to the function specified by definition, as generated by call.

expand.dots

logical. Should arguments matching ... in the call be included or left as a ... argument?

Value

• See the helpfiles for the system functions.

Details

Sometimes eval is used to execute statements in another frame. If such statements include calls to the system versions of these routines, the results will probably not be what you want. In technical terms: the same environment will actually appear several times on the call stack (returned by sys.frame()) but with a different calling history each time. The mvb. equivalents look through sys.frames() for the first frame whose environment is identical to the environment they were called from, and base all conclusions on that first frame. To see how in detail, look at the most fundamental function: mvb.sys.parent.

See Also

sys.parent, sys.nframe, parent.frame, match.call, nargs, sys.call, sys.function, sys.on.exit

Examples

ff.no.eval <- function() sys.nframe()
ff.no.eval() # 1
ff.system <- function() eval( quote( sys.nframe()), envir=sys.frame( sys.nframe()))
ff.system() # expect 1 as per ff.no.eval, get 3
ff.mvb <- function() eval( quote( mvb.sys.nframe()), envir=sys.frame( sys.nframe()))
ff.mvb() # 1
ff.no.eval <- function(...) sys.call()
ff.no.eval( 27, b=4) # ff.no.eval( 27, b=4)
ff.system <- function(...) eval( quote( sys.call()), envir=sys.frame( sys.nframe()))
ff.system( 27, b=4) # eval( expr, envir, enclos) !!!
ff.mvb <- function(...) eval( quote( mvb.sys.call()), envir=sys.frame( sys.nframe()))
ff.mvb( 27, b=4) # ff.mvb( 27, b=4)