R help - Oct 2014 - Befuddled by ddply

Folks,

I have the following data:

mdf<-structure(list(a = 1:3, b = c(10, 20, 30)), .Names = c("a",
"b"
), row.names = c(NA, -3L), class = "data.frame")

And function:

defCurveBreak<-function(x, y) {
  cumsum(rep(diff(c(0, x)), each = y)/y)
}

lapply'ing to get the result "foo"

foo<-data.frame(lapply(mdf, function(x, y) defCurveBreak(x,y),
4))
> foo
      a    b
1  0.25  2.5
2  0.50  5.0
3  0.75  7.5
4  1.00 10.0
5  1.25 12.5
6  1.50 15.0
7  1.75 17.5
8  2.00 20.0
9  2.25 22.5
10 2.50 25.0
11 2.75 27.5
12 3.00 30.0

Which all works fine. 

I was wondering is there a way to do this using ddply? Is there a reason to do
this using ddply rather than the above idiom?

I spent a bunch of time trying to figure out how to set it up in ddply (is that
the wrong tool?) to no avail.

Thanks for your time,
Best,
KW