Stack Traces

When a script fails with an exception message, that message provides a description of the problem, in terms that may or may not make immediate sense to you. An exception message appears along with something called a stack trace, which is a kind of history of method calls going back to the top-level script.

The script in Listing C.1 has a problem (besides being obfuscated, contrived, and otherwise useless, that is) that prevents it from running to completion.

Listing C.1. div0.rb
#!/usr/bin/env ruby

def foo
  return 4.0/baz(20)
end

def baz(n)
  sum = 0
  n.times do |i|
    sum += quux(i)
  end
  return n + sum
end

def quux(v)
  return 9/(5-v)
end

puts foo

The Ruby interpreter produces the following information when trying to run the script:

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