I'm working on a medium size C++ project (will probably end up around 50k lines) and I have to provide an interactive terminal interface. The program produces scientific data as an output and the interactive interface is to let a researcher tweak a visual representation of what's going to be calculated before actually completing the calculation.I'm not keen on interactive programs that define their own language since they're all different (leading to confusion) and if they support a lot of functions almost require the developer to implement a proper parser-interpreter for the syntax.I would also like the ability to define smart configuration files using this program (thus avoiding the need to externally script it).It seems to me that the correct answer is to implement an existing scripting language with its own support library that can make callbacks into C++. Since I've been playing with Common Lisp recently I decided to have a go at doing this using ECL (insanely overkill for my purposes) and I have bound functions into Lisp and built a Lisp REPL that is capable of executing these callbacks.Whilst this more or less works, this doesn't really seem to be the use-case ECL was designed for, since I have to make quite a lot of effort to extract the user's input in a safe manner, and I'm using very few of its features.This is not a request for a library suggestion (though I would happily accept those as well as an answer), but a methodology question. My users are not overly used to a lot of programming languages (the department uses primarily IDL), and it's uncommon that any other language is used.A full Common Lisp implementation seems like quite a sledgehammer to crack a nut and the syntax will be quite foreign to the users (which in many ways is what I wanted to avoid by using a pre-defined language).Am I looking at the problem of building a REPL-like environment from the wrong direction - should I instead build my program into a library and use an interactive language with FFI against it?Essentially:I want to add an REPL like system to my C++ program for the user to setup their data.I would rather avoid defining my own dialect/syntax/language for this purpose, instead using a ready-made interpreter and just calling back into C++It would be nice to have the ability to use it for smart configuration files, that have logic inside them (basic control flow and arithmetic).As easy to use as possible for non-programmers.If you have solved this problem/had a similar dilemma in the past I would be interested to hear your thoughts (I understand this is quite an opinion based subject).Thanks!
Design: Lisp (or other scripting language) as an interactive interface for C++?
c++;interfaces;scripting
First, you have a false dilemma.If your users are not programmers and know only IDL, any other language (custom or existing) will look foreign to them. But that does not mean that they cannot learn something else. In fact, you would say that this is not really a problem: you'll have to write a tutorial and point them to documentation and other materials. All the languages below have good documentation. Common Lisp is a standardized language.LuaThis is covered in another answer, but I would still recommend it. The language is made to be embedded, and works well with C++.PythonBoost.Python is a popular way of integrating C++ code and Python. From what I heard, it seems that Python and especially NumPy is also popular for scientific computing.ClaspEven if you don't intend to use Common Lisp, please have a look at CLASP (video), which is an implementation of Common Lisp for C++.A full Common Lisp implementation seems like quite a sledgehammer to  crack a nut and the syntax will be quite foreign to the users (which  in many ways is what I wanted to avoid by using a pre-defined  language).I see it the other way: instead of having half a language that barely works (this is not directed at above languages, but about custom ones), a full Common Lisp implementation gives you a stable and mature environment. I don't know what your scientific data is about, but your user could even work with Maxima directly from your environment, which has an infix syntax if you want.Library/FFIAm I looking at the problem of building a REPL-like environment from  the wrong direction - should I instead build my program into a library  and use an interactive language with FFI against it?This is a possible way to do it, but I honestly cannot say which way is better for you.