Joe Armstrong the co-designer of Erlang was asked about what he did in order to improve as a programmer.

Seibel: Is there anything that you have done specifically to improve your skill as a programmer?

Armstrong: No, I don’t think so. I learned new programming languages but not with the goal of becoming a better programmer. With the goal of being a better language designer, maybe.

I like to figure out how things work. And a good test of that is to implement it yourself. To me programming isn’t about typing code into a machine. Programming is about understanding. I like understanding things. So why would I implement a JPEG thing like we talked about earlier? It’s because I’d like to understand wavelet transforms. So the programming is a vehicle to understand wavelet transformations. Or why do I try to do an interface to X Windows? Because I wanted to understand how the X protocol worked.

It’s a motivating force to implement something; I really recommend it. If you want to understand C, write a C compiler. If you want to understand Lisp, write a Lisp compiler or a Lisp interpreter. I’ve had people say, “Oh, wow, it’s really difficult writing a compiler.” It’s not. It’s quite easy. There are a lot of little things you have to learn about, none of which is difficult. You have to know about data structures. You need to know about hash tables, you need to know about parsing. You need to know about code generation. You need to know about interpretation techniques. Each one of these is not particularly difficult. I think if you’re a beginner you think it’s big and complicated so you don’t do it. Things you don’t do are difficult and things you’ve done are easy. So you don’t even try. And I think that’s a mistake.

Seibel: Several of the folks I’ve talked to have recommended learning different programming languages because it gives you different perspectives on how to solve problems.

Armstrong: Languages that do different things. There’s no point learning lots of languages that all do the same thing. Certainly I’ve written quite a lot of JavaScript and quite a lot of Tcl and quite a lot of C and quite a lot of Prolog—well, an enormous amount of Prolog and an enormous amount of Fortran and an enormous amount of Erlang. And a bit of Ruby. A bit of Haskell. I sort of read all languages and I’m not fluent at programming them all. Certainly I can program in quite a lot of languages.

Coders at Work – Page 222 – Joe Armstrong