An R Function that Only Works When You Try to Debug it

hate.R

# Debugging in R is much better than many languages, but sometime it can be
# frustrating.  Here's a function that makes it even more frustrating --
# it only works when you try to debug it!

# The challenge:
### Write a function that, if the function has a browser in it, will execute
### every line correctly, but if it does not have a browser in it, it will
### error.

# The solution:

hate <- function() {
 if (length(grep("browser()", body(hate))) == 1) {
   stop("I hate you.")
 }
 "I returned fine."
}

# If you run it without a browser...

hate()
# Error in hate() : I hate you.

# ...But then add the browser.
hate <- function() {
 browser()
 if (length(grep("browser()", body(hate))) == 1) {
   stop("I hate you.")
 }
 "I returned fine."
}

> hate()
# Called from: hate()
# Browse[1]>
# debug at #3: if (length(grep("browser()", body(hate))) == 1) {
#    stop("I hate you.")
# }
# Browse[2]>
# debug at #6: [1] "I returned fine."
# Browse[2]>
# [1] "I returned fine."

body(hate) <- bquote({ getFunction("browser")(); .(body(hate)) })