Node.h

typedef enum {
    NullaryNode = 0,
    UnaryNode   = 1,
    BinaryNode  = 2,
    TernaryNode = 3
} NodeType;

typedef struct node_struct Node;
struct node_struct {
    int pheromoneA;
    int pheromoneB;
    NodeType type;
    union {
        struct {
            Node *next;
        };
        struct {
            Node *next;
            Node *prev;
        };
        struct {
            Node *nodeA;
            Node *nodeB;
            Node *nodeC;
        };
    };
};