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One of the biggest benefits of testing comes from writing the test prior to the implementation (TDD). In a statically typed language, your test won't compile un

One of the biggest benefits of testing comes from writing the test prior to the implementation (TDD). In a statically typed language, your test won't compile until the implementation is there, meaning this process is less accessible to you. Type systems focus on making sure you write the code correctly. They help not at all whether you're writing the correct code. In the end, this is on you, the developer, to express correctness in the type system. So the theory goes if you can define the problem correctly in, say, Haskel's type system, (up front, mind you), you may not even need any tests. But most systems are built with incomplete information. You can't know everything ahead of time. Often what is ultimately "correct" is to ship sooner rather than later, learning what is systemically correct as you go along. This is where dynamic languages do well.

dllthomas 11y ago
> But most systems are built with incomplete information. You can't know everything ahead of time. Often what is ultimately "correct" is to ship sooner rather than later, learning what is systemically correct as you go along. This is where dynamic languages do well. Again, my experience is that this is precisely where the type checker gives me the most help.
chadaustin 11y ago
Well, I've done lots of TDD in both Python/PHP/JS _and_ Haskell and C++, and I don't agree at all. I was the advocate for TDD at IMVU and built many of the test frameworks and core systems across all languages. You can definitely TDD Haskell, for example, with liberal use of "undefined" or "error". Same with C++: just throw an exception in code paths you haven't "explored" with tests yet. Also, the notion that because Haskell has a strong type system you don't need tests is a persistent myth. It's nice to have types to prove certain aspects of your program, but you still need a test suite in any significant project.
- dllthomas 11y ago
  > Also, the notion that because Haskell has a strong type system you don't need tests is a persistent myth. It's nice to have types to prove certain aspects of your program, but you still need a test suite in any significant project. I think that given a strong type system there exist tests you might otherwise write that you don't need. And I think that is sometimes confused for "given a strong type system, all tests are unnecessary" (which, in my opinion/experience, certainly does not hold), both by some people advocating type systems and by some people reacting to advocacy of type systems.

dllthomas 11y ago

> But most systems are built with incomplete information. You can't know everything ahead of time. Often what is ultimately "correct" is to ship sooner rather than later, learning what is systemically correct as you go along. This is where dynamic languages do well. Again, my experience is that this is precisely where the type checker gives me the most help.

chadaustin 11y ago

Well, I've done lots of TDD in both Python/PHP/JS _and_ Haskell and C++, and I don't agree at all. I was the advocate for TDD at IMVU and built many of the test frameworks and core systems across all languages. You can definitely TDD Haskell, for example, with liberal use of "undefined" or "error". Same with C++: just throw an exception in code paths you haven't "explored" with tests yet. Also, the notion that because Haskell has a strong type system you don't need tests is a persistent myth. It's nice to have types to prove certain aspects of your program, but you still need a test suite in any significant project.

dllthomas 11y ago
> Also, the notion that because Haskell has a strong type system you don't need tests is a persistent myth. It's nice to have types to prove certain aspects of your program, but you still need a test suite in any significant project. I think that given a strong type system there exist tests you might otherwise write that you don't need. And I think that is sometimes confused for "given a strong type system, all tests are unnecessary" (which, in my opinion/experience, certainly does not hold), both by some people advocating type systems and by some people reacting to advocacy of type systems.