[R] Bug in parse; memory access test forgotten ?

[Jean Coursol]

I was exploring the polynom library with students:

library(polynom)
x <- polynomial()
z <- (1+x)^100
f <- as.function(z)     #  => Segmentation fault  (with R-1.8.1 and R-1.9.0) !!!

Debugging at hand:

as.function.polynomial <- function (x, ...) 
{
    p <- x
    horner <- function(p) {
        a <- as.character(rev(unclass(p)))
        h <- a[1]
        while (length(a <- a[-1]) > 0) {
            h <- paste("x*(", h, ")", sep = "")
            if (a[1] != 0) 
                h <- paste(a[1], " + ", h, sep = "")
        }
        h
    }
    f <- function(x) NULL
    body(f) <- parse(text = horner(p))[[1]]
    f
}

horner <- function(p) {
        a <- as.character(rev(unclass(p)))
        h <- a[1]
        while (length(a <- a[-1]) > 0) {
            h <- paste("x*(", h, ")", sep = "")
            if (a[1] != 0)
                h <- paste(a[1], " + ", h, sep = "")
        }
        h
}

x <- polynomial()
z <- (1+x)^100
zh <- horner(z)

nchar(zh)
[1] 2404

parse(text = zh) # => Segmentation fault (it ran one time !!!)

# The R solution (VR S programming p 95)

as.function.polynomial <- function(p) {
         function(x) { v <- 0; for (a in rev(p)) v <- a + x*v; v }
         }
# is running perfectly...

Jean Coursol