G'day all.
Quoting Sébastien Pierre
I am still unsure of whether Haskell would be a good competitor against other languages in my case, but it seems like if it does the best option would be to reuse C++ graph libraries and carefully write a wrapper around them to minimize passing values between C and Haskell worlds.
As a matter of curiosity, have you considered prototyping your program in Haskell first, and then subsequently translating it into C++? (Boost.Graph is supposed to be quite good, incidentally.) If Haskell provides more rapid development (and I think it does), then you can spend time in Haskell making your algorithms work, finding the "hot spots" and generally optimising it, then translating parts of it into C++ as needed. Cheers, Andrew Bromage