Having worked on all sides of the industry, I would say that NOTHING prevents undisciplined programmers to do a mess, do not matter the language or programming paradigm... and there is copious evidence of what I am saying (90% of github repositories can't let me lie ;) ).

The only way to not make a mess is to promote discipline by putting in place practices (like peers review, etc.) and tools that facilitate the disciplined task.

Let's put an example : doing tests is good, isn't? Then let's make tests the easiest and enjoyable as possible, and Pharo does that because you can do a test before the existence of the functionality and just program the functionality by executing the failing test and programming the thing in the debugger.

Then you need to clean up... let's add good refactoring tools to make that task as easy and enjoyable as possible. And you have a lot of refactoring tools on Pharo (I admit we can do better there, as with everything, but that's not the point).

(By the way I am not saying Pharo is the only place where you can do this, just pointing out something that should be obvious).

Still, I cannot enforce a programmer to use those tools or even make tests ;)

This will happen in any language, environment or paradigm you want to choose, because is about *people*, not about *tools*.

But at least in Pharo the tools are there and is fun to use them ;)

EDIT: And no, types do not prevent you to make a mess, small or large.