Typed vs Dynamic Programming Languages

Those days I work a lot in the Javascript world and Typescript—a typed version of javascript—is becoming more and more popular. Some of my coworkers also promote it strongly and they can not see the point of using a dynamic language anymore.

Usually those are the selling points:

• The extra security provided by types is to be too be important to be passed on.
• Types help with refactoring.
• Types make it easier to provide better programming tools.

Pro dynamic languages programmers will usually tell you that with dynamic languages:

• It is easier to get started
• You have less constraints on dependencies.
• Deployment is easier

Those are all valid points. More importantly, it seems there is always a cycle between typed languages and dynamic languages. And this cycle, this repeating history seems more important as it illustrates the real life benefits of both.

Lets imagine the life of Mr IKnowNothing. Mr IKnowNothing starts his career as a novice programmer. As he starts on his first job he uses `Haskell`. `Haskell` is a typed language. He starts writing some code and he is very happy as the `Haskell` compiler helps correct his program as he writes it. He could never consider writing something in a non-typed language as the types are helping him so much.

However after some times, Mr IKnowNothing discovers that there are still some bugs in his program. For example consider

addTwo :: Integer -> Integer
addTwo x = x + 1

addTwo 2

3

This is perfectly valid Haskell, it compiles, however Mr IKnowNothing made a typo and it adds 1 instead of 2. It is not enough that the code pass compile. The behaviour of the code is also important.

Mr IKnowNothing is pretty disappointed so he decides to start writing some tests. Eventually as he becomes more skilled he writes more and more tests and write code with less and less bugs. All is fine except that he has a breakthrough.

Here is a thought from Mr IKnowNothing:

If I need to write tests for all of my code anyway, why should I use types? Could I not just use dynamic languages? If I have enough tests I don't need all of those type annotations and I can write and deploy programs even faster.

So Mr IKnowNothing starts using a dynamic programming language. He tests extensively his code. He deploys. Everything works, he has never been so productive. Everything is fine, at least for a time…

Here comes a new Hire, Miss IWantToLearn. She is a beginner programmer just as was Mr IKnowNothing. And Mr IKnowNothing is pretty disappointed with Miss IWantToLearn. She makes so many mistakes!

Well let me say this. Mr IKnowNothing is very unfair. Miss IWantToLearn did not have time to learn how to program with the protection of a typed language. Of course she is going to make a lot of mistakes. Mr IKnowNothing still makes a lot of mistakes after all.

As a natural side effect Miss IWantToLearn is very dissapointed with this dynamic programming language. Also at this recent meetup she has learned about this cool typed language called `Rust` and it seems that `Rust` is a very safe language. There is no way she will use anything else than a typed language from now on.

Miss IWantToLearn moves to a typed language until she realizes like Mr IKnowNothing that she also needs test. And history repeats…

If you see this evil circle, break it. Be aware of which kind of programming language you use and why you use it.

For example:

• If I were to go on Mars with my life depending on my

software I would use typed programming with an extensive suite of tests.

• Most of my coworkers are less experienced than me? Let's use typed programming as it will help them. At the same time let's introduce them to testing.
• You are an expert team of 3 or 5 programmers? Use a dynamic language and use it to ship something quicky. If your tests are good enough it will work!

Of course there are variations around this theme and there are different ways to `test` your program but this is the gist of the problem.

Move away from people that don't really understand the two alternatives and that are two religious about the choice. Pick the correct programming language best on your team strengths.