fpcpp

fpcpp (functional programming in C++) is a lightweight, header-based C++ library for enabling functional programming style and features in modern C++ programs.

Example

Generate pi using Monte Carlo sampling:

double pi(size_t samples = 1000) {    

    return 4.0 * length(filter([](double d) { return d <= 1.0; }, 
                               map([](const pair<double,double>& p) { return fst(p)*fst(p) + snd(p)*snd(p); },
                                   zip(take(samples, uniform(-1.0,1.0)),
                                       take(samples, uniform(-1.0,1.0))))) / samples;
                                       
}

or

double pi(size_t samples = 1000) {

    let sampler = []() -> int { 
        let x = uniform(-1.,1.); 
        let y = uniform(-1.,1.);
        let dist2 = x*x + y*y;
        return dist2 < 1. ? 1 : 0;
    };

    return 4. * foldl1(addF(), take(samples, sampler)) / samples;
    
}

Map an operation across a filtered source and check for success:

template<typename SuccessOp, typename MapOp, typename FilterOp, typename Source> {
bool filteredMap(SuccessOp, MapOp mapOp, FilterOp filterOp, Source source) { 
    using namespace fp;
    return all(successOp,
               map(mapOp,
                   filter(filterOp,
                          source)));

Curry functions:

let multiplyBy4 = curry(multiplyF()), 4);
let twentyEight = multiplyBy4(7);

Compose functions:

// l1 norm = |x|+|y| = f(g(x),g(y)) where f = add, g = abs

let l1   = compose2(addF(), absF(), absF());
assert( l1(1.f, -2.f) == 3.f );


// l2 norm = sqrt(x*x + y*y) = f(g(h(x),h(y))) where f = sqrt, g = plus, h = square

let square = [](float x) { return x*x; };
let l2 = compose(sqrtf, compose2(addF(), square, square));
assert( l2(3.f, 4.f) == 5.f );

Documentation

Please see the file called INSTALL for usage details.
Several samples and tests are included with the source; together with CMake, these can be built and run with any compatible compiler (developed with VC10, tested on GCC 4.6).

Licensing

MIT. Please see the file called LICENSE.

Contributions

This project was directly inspired by late-night encounters with Haskell. FC++ (http://sourceforge.net/projects/fcpp/) is an excellent library for pre-C++11 functional programming endeavors.