[Jach]

For your example bug I think you're wrong that static types would have made the bug impossible. What you need is strong type checking and a lack of auto-conversion. For example, in Java, this compiles:

    int[] bodies = {1, 2, 3};
    for (int body : bodies) {
        String formatted_body = "<p>" + body + "</p>";
        callMethodWithStrArg(formatted_body);
    }

And if in this hypothetical case it was previously a `String[] bodies` and a `String body`, I bet a lot of programmers would use an auto-refactoring tool because "static types and auto-refactoring go together for being confident in changes like apples and pie" and I bet the error wouldn't have been noticed even at review time. God help you if you're using a static language without generics that has implicit type conversions. In Python, though, this raises an error:

    bodies = [1, 2, 3]
    for body in bodies:
      formatted_body = '<p>' + body + '</p>'

The error is: "TypeError: cannot concatenate 'str' and 'int' objects".

Dynamically typed languages still have types.

[david-given]

That's very true (and I really wish that Lua didn't do implicit type conversion of numbers to strings --- it's a major wart on an otherwise very nice language).

I had totally forgotten that Java does it too, despite having done `""+i` lots of times as a cheap and easy and evil way to convert numbers to strings.

...I am currently rewriting a big chunk of the primary data storage to use immutable data structures, because it makes implementing Undo easier. I am having to fight the urge to redo it all in Haskell.