call default args

[Michael Schubert]

In io/text: the .set_defaults function should be moved to be generally accessible, as matching default args in a call is a task that will occur more often (I'm working on something now, for instance).

.set_defaults = function (call, .formals = formals(sys.function(sys.parent()))) {
    for (n in names(.formals))
        if (n != '...' && ! (n %in% names(call)))
            call[[n]] = .formals[[n]]

    call
}

The method also fails for functions with NULL arguments, like the one below.

x = function(y=NULL) {
    args = .set_defaults(match.call())
    as.list(args)
} 
# > x()
# Error in call[[n]] = .formals[[n]] : subscript out of bounds

[Michael Schubert]

@klmr any chance to get this done.. err.. today?

[Konrad Rudolph]

I’m on it, as I agree.

[Michael Schubert]

some preliminary code to consider that does what I need (basically, just match.call() with defaults):

match_call_defaults = function (call = match.call(sys.function(sys.parent())),
            .formals = formals(sys.function(sys.parent()))) {
    call = as.list(call)[-1]
    .formals = .formals[names(.formals) != '...']

    for (n in names(call))
        .formals[[n]] = call[[n]]

    .formals
}

[Konrad Rudolph]

I was going to suggest something very similar.

[Konrad Rudolph]

Err, scratch that, your function does something else entirely. My function returns a call object that can be eval’d. Yours doesn’t. I’m not exactly sure which purpose your function vs. mine should fulfill.

[Michael Schubert]

Yes, the two are semantically different but structurally similar. Mine should get all arguments of the function call (including default arguments) as a list.

[Konrad Rudolph]

Ah, shame: I’d tried using a loop-less code:

match_call_defaults = function (call = match.call(sys.function(sys.parent()), sys.call(sys.parent())),
                                .formals = formals(sys.function(sys.parent()))) {
    .formals = .formals[names(.formals) != '...']
    new_call = as.call(c(call[[1]], .formals))
    new_call[names(call[-1])] = call[-1]
    new_call
}

But this fails to expand ... in the call. So:

(function (...) match_call_defaults())(1, 2, 3)

ends up with an empty argument list.