[R] scoping problem

I would like to write a function that computes Tukey's 1 df for nonadditivity. Here is a simplified version of the function I'd like to write: (m is an object created by lm): tukey.test <- function(m) { m1 <- update(m, ~.+I(predict(m)^2)) summary(m1)$coef } The t-test for the added vari

[R] Evaluating args in a function

Can anyone explain what I'm doing wrong here: > fred <- data.frame() > class(fred) [1] "data.frame" > test.fn <- function(x,class=class(x)) {class} > test.fn(fred) Error in test.fn(fred) : promise already under evaluation: recursive default argument reference or earlier problems? R 2.5.1 on