There were three things that really did it for me: powerful macro's + language designed to be easily macro'd; incremental compilation; updating live code. The macro's let me extend it however I liked. OOP was invented? Add a library. Aspects? Add a library. Type-checking? Add a library. In each case, the language itself transforms to more effectively use the approach with much zero-overhead potential given the transforms are usually at compile-time. I had DSL's for common things such as GUI's, state-machines, and databases. Let me do so much with so little work while having consistency across the whole thing.
The second was incremental compilation. I was an imperative programmer and mostly used that style. Languages such as C++ interrupt one's mental flow with long compile cycles. Interactive languages, especially scripting, tended to be too slow in production. LISP let me compile individual functions in a fraction of a second after writing them. Think, type, hit button, examine results, and repeat. The flow stays there and you just keep pumping out more of your solution. That my main DSL was compatible with a C++ subset meant I could just autogenerate that at the end to benefit from its compilers or portability. Otherwise, I stayed in LISP.
The third thing was something that I tried with C/C++. Self-modifying code for AI and security applications was one use. Another was updating apps live. LISP made both pretty easy. The program ran as an instance while you made it in certain development environments. You were in a way always working with a live program. Also, you could drop a member variable in a class definition and all running instances of that class would loose it. Just like that. So easy to change while being able to compile to fast code with type & safety level declarations.
So, it was a language that could do anything I want it to do, allow rapid iterations at max flow, and even change running systems if they weren't good enough. Still haven't felt this full effect in other languages. The old LISP machines went further [1] in that they could take you to any problem in the app or OS right at the source code without crashing. Like LISP apps, you can inspect the issue, modify the code of the running system, optionally modify the instance, and proceed how you wanted to. Still waiting for that feature in Windows or Linux development. ;)
The second was incremental compilation. I was an imperative programmer and mostly used that style. Languages such as C++ interrupt one's mental flow with long compile cycles. Interactive languages, especially scripting, tended to be too slow in production. LISP let me compile individual functions in a fraction of a second after writing them. Think, type, hit button, examine results, and repeat. The flow stays there and you just keep pumping out more of your solution. That my main DSL was compatible with a C++ subset meant I could just autogenerate that at the end to benefit from its compilers or portability. Otherwise, I stayed in LISP.
The third thing was something that I tried with C/C++. Self-modifying code for AI and security applications was one use. Another was updating apps live. LISP made both pretty easy. The program ran as an instance while you made it in certain development environments. You were in a way always working with a live program. Also, you could drop a member variable in a class definition and all running instances of that class would loose it. Just like that. So easy to change while being able to compile to fast code with type & safety level declarations.
So, it was a language that could do anything I want it to do, allow rapid iterations at max flow, and even change running systems if they weren't good enough. Still haven't felt this full effect in other languages. The old LISP machines went further [1] in that they could take you to any problem in the app or OS right at the source code without crashing. Like LISP apps, you can inspect the issue, modify the code of the running system, optionally modify the instance, and proceed how you wanted to. Still waiting for that feature in Windows or Linux development. ;)
[1] http://www.symbolics-dks.com/Genera-why-1.htm