Pure.h use-case

pure-test.cpp

#include <functional>
#include <algorithm>
#include <vector>
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <iterator>

using namespace std;
using namespace placeholders;

#define RNG(seq) seq.begin(), seq.end()

void print( const char* const msg, const vector<int>& v )
{
    cout << msg << "\n";
    copy( RNG(v), ostream_iterator<int>(cout, " ") );
    cout << "\n\n";
}

template< typename Printable >
void print_val( const char* const msg, const Printable& p )
{
    cout << msg << '\n' << p << "\n\n";
}

bool even( int x )
{
    return x % 2 == 0;
}

vector<int> qsort( vector<int> v )
{
    const int pivot = v.front();
    return ordered(v) ? v
        : concat (
            qsort( filter([=](int x){return x< pivot;}, v) ),
            qsort( filter([=](int x){return x==pivot;}, v) ),
            qsort( filter([=](int x){return x> pivot;}, v) )
        );
}

int main()
{
    vector<int> a(10);

    iota( RNG(a), 1 );
    print( "a = [ x | x <- [1..10] ]", a );

    vector<int> fib(10,1);
    transform( fib.begin(), fib.end() - 2, // src 1
               fib.begin() + 1,            // src 2
               fib.begin() + 2,            // dest
               plus<int>() );
    print( "fib 0 = 1\nfib 1 = 1\nfib x = fib (x-1) fib (x-2)", fib );

    vector<int> b;
    transform( RNG(a), back_inserter(b), bind( plus<int>(), _1, 4) );
    print( "map (+4) a", b );

    vector<int> c;
    auto end = copy_if( RNG(a), back_inserter(c), even );
    print( "filter even a", c );

    bool allof = all_of( RNG(c), even );
    print_val("all even (filter even a)", allof? "t" : "f" );

    auto x = accumulate( RNG(a), 2, multiplies<int>() );
    print_val( "foldl (*) 2 a", x );

    vector<int> outOfOrder = { 2, 5, 3, 1 };
    print_val( "maximum [2,5,3,1]", *max_element(RNG(outOfOrder)) );

    srand( time(0) );
    vector<int> randoms(10); generate( RNG(randoms), &rand );
    print( "g <- getStdGen\n"
           "qsort $ take 10 (randoms g)::[Int]", qsort(randoms) );

    // Currying.
    auto prnt = bind( print, "...", _1 );
    prnt(a); prnt(b);
}