Python. I find I can more-or-less do intermediate-level design using the prototyping language, fleshing things out in successive passes, until it actually work

Python. I find I can more-or-less do intermediate-level design using the prototyping language, fleshing things out in successive passes, until it actually works. Dynamic typing means it's easy to evolve the particulars without needing massive amounts of syntax. And the massive number of available packages means that for most projects, you're starting from a pretty high base. Subsequent translation of parts or all of the system into C, C++, Java, etc, is usually largely mechanical. Progressively replacing the performance-critical bits with C/C++ is helpful too. It's also possible to write testing harnesses, etc, in Python once the prototype is running, using them to find and fix corner cases, and then keep those same tests for the production version. I fund that 3-step (prototype, tests, production) process quite effective.