Question

If you had the possibility of having an application that would use both Haskell and C++.
What layers would you let Haskell-managed and what layers would you let C++-managed ?

Has any one ever done such an association, (surely) ?

(the Haskell site tells it’s really easy because Haskell has a mode where it can be compiled in C by gcc)

At first I think I would keep all I/O operations in the C++ layers. As well as GUI management.

It is pretty vague a question, but as I am planning to learn Haskell, I was thinking about delegating some work to Haskell-code (I learn in actually coding), and I want to choose some part where I will see Haskell benefits.

Answer 1

The benefit of Haskell is the powerful abstractions it allows you to use. You’re not thinking in terms of ones and zeros and addresses and registers but computations and type properties and continuations.

The benefit of C++ is how tightly you can optimize it when necessary. You aren’t thinking about high-minded monads, arrows, partial application, and composing pure functions: with C++, you can get right down to the bare metal!

There’s tension between these two statements. In his paper “Structured Programming with go to statements,” Donald Knuth wrote

I have felt for a long time that a talent for programming consists largely of the ability to switch readily from microscopic to macroscopic views of things, i.e., to change levels of abstraction fluently.

Knowing how to use Haskell and C++ but also how and when to combine them well will knock down all sorts of problems.

The last big project I wrote that used FFI involved using an in-house radar modeling library written in C. Reimplementing it would have been silly, and expressing the high-level logic of the rest of the application would have been a pain. I kept the “brains” of it in Haskell and called the C library when I needed it.

You’re wanting to do this as an exercise, so I’d recommend the same approach: write the smarts in Haskell. Shackling Haskell as a slave to C++ will probably end up frustrating you or making you feel as though you wasted your time. Use each language where its strengths lie.