struct Ast_Node;

typedef enum {
    Ast_Node_Type_Nil,

    Ast_Node_Type_Symbol,
    Ast_Node_Type_Keyword,
    Ast_Node_Type_Number,
    Ast_Node_Type_String,

    Ast_Node_Type_Pair,
    Ast_Node_Type_Function,
    Ast_Node_Type_Built_In_Function,
} Ast_Node_Type;

typedef struct {
    char* identifier;
} Symbol;

typedef struct {
    char* identifier;
} Keyword;

typedef struct {
    double value;
} Number;

typedef struct {
    char* value;
} String;

typedef struct {
    struct Ast_Node* first;
    struct Ast_Node* rest;
} Pair;

typedef struct {
    Pair* regular_params;
    Pair* keyword_params;
} Lambda_List;

typedef struct {
    Lambda_List* parameters;
    Pair* form;
} Function;

typedef struct {
    char* identifier;
} Built_In_Function;

struct Ast_Node {
    Ast_Node_Type type;
    union {
        Symbol*   symbol;
        Keyword*  keyword;
        Number*   number;
        String*   string;
        Pair*     pair;
        Function* function;
        Built_In_Function* built_in_function;
    } value;
};
// was forward declarated
typedef struct Ast_Node Ast_Node;


Ast_Node* create_ast_node_nil() {
    Ast_Node* node = new(Ast_Node);
    node->type = Ast_Node_Type_Nil;
    node->value.pair = NULL;
    return node;
}

Ast_Node* create_ast_node_number(double number) {
    Ast_Node* node = new(Ast_Node);
    node->type = Ast_Node_Type_Number;
    node->value.number = new(Number);
    node->value.number->value = number;
    return node;
}

Ast_Node* create_ast_node_string(char* str) {
    Ast_Node* node = new(Ast_Node);
    node->type = Ast_Node_Type_String;
    node->value.string = new(String);
    node->value.string->value = str;
    return node;
}

Ast_Node* create_ast_node_symbol(char* identifier) {
    Ast_Node* node = new(Ast_Node);
    node->type = Ast_Node_Type_Symbol;
    node->value.symbol = new(Symbol);
    node->value.symbol->identifier = identifier;
    return node;
}


Ast_Node* create_ast_node_built_in_function(char* identifier) {
    Ast_Node* node = new(Ast_Node);
    node->type = Ast_Node_Type_Built_In_Function;
    node->value.built_in_function = new(Built_In_Function);
    node->value.built_in_function->identifier = identifier;
    return node;
}

Ast_Node* create_ast_node_pair(Ast_Node* first, Ast_Node* rest) {
    Ast_Node* node = new(Ast_Node);
    node->type = Ast_Node_Type_Pair;
    node->value.pair = new(Pair);
    node->value.pair->first = first;
    node->value.pair->rest = rest;
    return node;
}