Compiling higher level languages to lower level ones is cake. There’s countless examples of it being done. Without going off on much of a tangent, we can point to early C++ compilers that compiled down to C.

When you start throwing “clean” and “readable” into the mix, however, things get really tough. Clean, readable code expresses the meaning and intent of what you were writing. Computers are notoriously bad at interpreting & creating meaning. You’re more likely to end up with variables named int_147 than input_buffer_length. Sure, if you really wanted to make this project work, you could engage in a massive AI project to handle converting your Lisp to some sort of decently readable C++ but, to be perfectly honest, Common Lisp compilers are pretty fucking good at what they do.

More important than the difficulty of generating C++ from a Lisp is the usefulness of this. What purpose would it serve for the generated C++ to be readable? If the Lisp is your source code, intermediate representations should be irrelevant. If you want to be able to hand the C++ over to programmers that don’t understand your original Lisp, you’ve now got another problem. What happens when they want to modify your generated C++? What happens if they write things in C++ that don’t cleanly translate to your Lisp?

Let’s say we’ve solved that. It’s a decade later and, after burning through hundreds of millions of dollars of DoD grant money, we’ve build this massive, complex (but flawless) language translation engine that can turn Lisp into idiomatic C++ and vice versa. What have we really gained that wouldn’t be better accomplished by either teaching people a new programming language or just developing a new compiler that lets us link the two languages?

Oh, right. Your boss wants you to write C++ and you’d rather not. Update your resume & find a new job.

Short answer, there is nothing out there currently that will help you convert Lisp to READABLE C++. Sure you can convert anything to C++ or C but readable code is written by humans, not programs. Sure you can output C++ code with proper formatting, indents, nice class names, and maybe even somehow get perfect translation from Lisp class objects to C++ classes. Maybe you can get your library dependencies linked just right, and maybe you can compile binaries that are very close to what the C language would have produced had you written the whole thing in C. But ultimately, readable code is a beauty that is not understood by anyone, at least not just yet, and possibly never considering that the term readable is quite subjective to begin with and what might be considered readable among one group of developers may be considered atrocious by others.

To make C++ readable, you have to write in C++, not in Lisp. You also have to be able to change your coding style according to what the people who will read your code will best understand. Just like books, programs are written with a specific audience in mind and can be beautiful and touching if written well, and obfuscated and tedious if not. And if we can’t come up with a program to write beautiful fiction novels for us, then we won’t be able to come up with something to convert to readable C++.

ViM is a great IDE for C++. It has the best completion I’ve ever seen so far too, though it gets a little slow if you pull in a lot of headers, the clang complete. And for compilation I found all IDEs lacking anyway; you end up writing build system in CMake or something anyway. And I have not seen anything to provide any help for lisp, period.

True, C++ does not have lisp-style macros, but templates can do everything scheme’s hygienic macros can and some more, because you can implement them differently based on types and based on their capabilities. True, it’s lack of garbage collector makes closures a bit more tedious, but the RAII idiom used for resource management instead has it’s own advantages and interesting properties.

If you are a student, do you really know all the advanced C++? From algorithms library over writing templates with alternate implementations based on properties of argument types, compile time calculations using template meta-programming (using Boost.MPL) to understanding how Boost works under the hood? If not, I recommend taking this as opportunity to learn some advanced C++. School assignment won’t need to be maintained, so you can play with the language to see what the features are worth where in production code you’d have to be careful about readability.

And to answer the final direct question: C++ has so many more idioms under it’s belt that there is no way to generate idiomatic C++ from anything. Simply because there will be no way to express most of those idioms in anything else. Starting from the fact that anything will garbage collection will allocate everything on heap while in C++ it is idiomatic to take advantage of the stack.