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This is an excerpt of a post that I wrote for Olio Apps.

I am always interested in making my coding process faster and more robust. I want to be confident that my code will work as expected. And I want to spend as little time as possible debugging, testing, and hunting down pieces of code that I forgot to update when I make changes to a project. That is why I am a fan of correct-by-construction methods. Those are methods of constructing programs where the program will not build / compile unless it behaves the way that it is supposed to.

Correct by construction

Test-driven development is one form of correct-by-construction method. The philosophy of test-driven development is that your tests are the specification for how your program should behave. If you look at your test suite as a mandatory part of your build process, if your tests do not pass the program does not build because it is not correct. Of course the limitation is that the correctness of your program is only as certain as the completeness of your tests. Nevertheless studies have found that test-driven development can result in 40%-80% fewer bugs in production.

Writing your program around types

Type-driven development is the practice of writing your program around types, and of choosing types that make it easy for the type checker to catch logic errors. In type-driven development your data types and type signatures are the program specification. Types also serve as a form of documentation that is guaranteed to be up-to-date. Type-driven development is another correct-by-construction method. As with test-driven development, type-driven development can improve your confidence in your code, and can save you time when making changes to a large codebase.

» Read the rest on the Olio Apps blog.