when/unless/go keywords

when.cpp

// when/unless go/unless keywords
// - rlyeh

#include <functional>
#include <iostream>

#define when(...)   for( std::function<void()> fn; !fn && (__VA_ARGS__ +0); fn() ) fn = [&]
#define unless(...) , !(__VA_ARGS__) ? fn : fn = [&]
#define go          when(true)

// sample

struct player_t {
    int type = 0;
    enum { BATMAN = 0, CATWOMAN = 1 };
    bool in_shadow = 0;
};

struct enemy_t {
    int type = 0;
    int gang = 1;
    bool something_on_fov = 1;
    int health = 100;
    enum { HUMAN = 0, PENGUIN = 1 };
    void say( const char *text ) {
        std::cout << text << std::endl;
    }
};

int main() {
    player_t player;
    enemy_t enemy, poison_ivy;

    // original expression :
    auto eval = [&] {
        when( enemy.something_on_fov ) {
            enemy.say("guys! it's batman!!!"); 
        }
        unless( !enemy.gang ) { enemy.say("oh no batman! please don't hurt me"); }
        unless( enemy.type == enemy_t::PENGUIN ) { enemy.say("kwak! kwak! i think i see batman!"); }
        unless( player.in_shadow ) { enemy.say( "hmmm... i think i see batman!"); }
        unless( player.type == player_t::CATWOMAN ) { enemy.say("it's the kitty kat!"); }
        unless( player.type == player_t::CATWOMAN && poison_ivy.health > 0 ) { enemy.say("hey cat, the boss wants a word with you..."); }
        ;
    };

    // gets translated into:
    auto eval1 = [&] {
        for( std::function<void()> fn; !fn && (enemy.something_on_fov); fn() ) 
            fn = [&] {
                enemy.say("guys! it's batman!!!"); 
            }
            , !( !enemy.gang) ? fn : fn = [&]{ enemy.say("oh no batman! please don't hurt me"); }
            , !( enemy.type == enemy_t::PENGUIN) ? fn : fn = [&]{ enemy.say("kwak! kwak! i think i see batman!"); }
            , !( player.in_shadow ) ? fn : fn = [&]{ enemy.say( "hmmm... i think i see batman!"); }           
            , !( player.type == player_t::CATWOMAN) ? fn : fn = [&]{ enemy.say("it's the kitty kat!"); }
            , !( player.type == player_t::CATWOMAN && poison_ivy.health > 0) ? fn : fn = [&]{ enemy.say("hey cat, the boss wants a word with you..."); } 
            ;
    };

    player = player_t();
    eval();

    player = player_t(); enemy.gang = 0;
    eval();

    player = player_t(); player.in_shadow = 1;
    eval();

    for( unsigned i = 1; i <= 100; ++i ) {
    	go {
    		std::cout << i << ',';
    	}
    	unless( 0 == i % 3 ) {
    		std::cout << "fizz,";    		
    	}
    	unless( 0 == i % 5 ) {
    		std::cout << "buzz,";    		
    	}
    	unless( 0 == i % 15 ) {
    		std::cout << "fizzbuzz,";    		
    	};
    }
}