Ast_Node* eval_expr(Ast_Node* node, Environment* env);

Ast_Node* apply_arguments_to_function(Ast_Node* arguments, Function* function, Environment* parent) {
    // NOTE(Felix): if it is a macro, we will set it later, so we can
    // use the default "define_symbol" method here instead of
    // switching between "define_symbol" and "define_macro_symbol" all
    // the time

    Environment* new_env = create_child_environment(parent, Environment_Type_Lambda);

    // positional arguments
    for (int i = 0; i < function->positional_arguments->next_index; ++i) {
        if (arguments->type == Ast_Node_Type_Pair) {
            // TODO(Felix): here we create new ast_node_symbols from
            // their identifiers but before we converted them to
            // strings from symbols... Wo maybe just use the symbols?
            define_symbol(
                create_ast_node_symbol(function->positional_arguments->identifiers[i]),
                arguments->value.pair->first, new_env);
        } else {
            // not enough arguments given
            create_error(Error_Type_Ill_Formed_Arguments, arguments);
            return nullptr;
        }
        arguments = arguments->value.pair->rest;
    }

    if (arguments->type == Ast_Node_Type_Nil)
        goto eval_time;

    String_Array_List* read_in_keywords = create_String_array_list(16);
    // keyword arguments: use all given ones and keep track of the
    // added ones (array list), if end of parameters in encountered or
    // something that is not a keyword is encountered or a keyword
    // that is not recognized is encoutered, jump out of the loop.

    while (arguments->value.pair->first->type == Ast_Node_Type_Keyword) {
        // check if this one is even an accepted keyword
        bool accepted = false;
        for (int i = 0; i < function->keyword_arguments->next_index; ++i) {
            if (string_equal(
                    arguments->value.pair->first->value.keyword->identifier,
                    function->keyword_arguments->identifiers[i]))
            {
                accepted = true;
                break;
            }
        }
        if (!accepted) {
            create_error(Error_Type_Ill_Formed_Arguments, arguments);
            return nullptr;
        }

        // check if it was already read in
        for (int i = 0; i < read_in_keywords->next_index; ++i) {
            if (string_equal(
                    arguments->value.pair->first->value.keyword->identifier,
                    read_in_keywords->data[i]))
            {
                // TODO(Felix): if we are actually done with all the
                // necessary keywords then we have to count the rest
                // as :rest here, instead od always creating an error
                // (special case with default variables)
                create_error(Error_Type_Ill_Formed_Arguments, arguments);
                return nullptr;
            }
        }

        // okay so we found a keyword that has to be read in and was
        // not already read in, is there a next element to actually
        // set it to?
        if (arguments->value.pair->rest->type != Ast_Node_Type_Pair) {
            create_error(Error_Type_Ill_Formed_Arguments, arguments);
            return nullptr;
        }

        // if not set it and then add it to the array list
        define_symbol(
            create_ast_node_symbol(arguments->value.pair->first->value.keyword->identifier),
            arguments->value.pair->rest->value.pair->first, new_env);

        append_to_String_array_list(read_in_keywords, arguments->value.pair->first->value.keyword->identifier);

        // overstep both for next one
        arguments = arguments->value.pair->rest->value.pair->rest;

        if (arguments->type == Ast_Node_Type_Nil) {
            break;
        }
    }


    // check if all necessary keywords have been read in
    for (int i = 0; i < function->keyword_arguments->next_index; ++i) {
        char* defined_keyword = function->keyword_arguments->identifiers[i];
        bool was_set = false;
        for (int j = 0; j < read_in_keywords->next_index; ++j) {
            if (string_equal(
                    read_in_keywords->data[j],
                    defined_keyword))
            {
                was_set = true;
                break;
            }
        }
        if (function->keyword_arguments->values->data[i] == nullptr) {
            // if this one does not have a default value
            if (!was_set) {
                create_error(Error_Type_Ill_Formed_Arguments, arguments);
                return nullptr;
            }
        } else {
            // this one does have a default value, lets see if we have
            // to use it or if the user supplied his own
            if (!was_set) {
                define_symbol(
                    create_ast_node_symbol(defined_keyword),
                    function->keyword_arguments->values->data[i], new_env);
            }
        }
    }


    if (arguments->type == Ast_Node_Type_Nil) {
        if (function->rest_argument) {
            define_symbol(
                create_ast_node_symbol(function->rest_argument),
                create_ast_node_nil(), new_env);
        }
    } else {
        if (function->rest_argument) {
            define_symbol(
                create_ast_node_symbol(function->rest_argument),
                arguments, new_env);
        } else {
            // rest was not declared but additional arguments were found
            create_error(Error_Type_Ill_Formed_Arguments, arguments);
            return nullptr;
        }
    }

  eval_time: {
        Ast_Node* result;

        // don't have to check every time if it is macro environment or
        // not
        if (function->is_macro)
            new_env->type = Environment_Type_Macro;

        try {
            result = eval_expr(function->body, new_env);
        }

        free(new_env);
        return result;
    }
}

/*
   (prog
     (define type--before type)
     (define type
       (lambda (e)
         (if (and (= (type--before e) :pair) (= (first e) :my-type))
             :my-type
           (type--before e))))
   )
*/

/**
   This parses the argument specification of funcitons into their
   Function struct. It dois this by allocating new
   positional_arguments, keyword_arguments and rest_argument and
   filling it in
*/
void parse_argument_list(Ast_Node* arguments, Function* function) {
    // first init the fields
    function->positional_arguments = create_positional_argument_list(16);
    function->keyword_arguments    = create_keyword_argument_list(16);
    function->rest_argument        = nullptr;

    // okay let's try to read some positional arguments
    while (arguments->type == Ast_Node_Type_Pair) {
        if (arguments->value.pair->first->type == Ast_Node_Type_Keyword) {
            if (string_equal(arguments->value.pair->first->value.keyword->identifier, "keys") ||
                string_equal(arguments->value.pair->first->value.keyword->identifier, "rest"))
                break;
            else {
                create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
                return;
            }
        }

        if (arguments->value.pair->first->type != Ast_Node_Type_Symbol) {
            create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
            return;
        }

        // okay wow we found an actual symbol
        append_to_positional_argument_list(
            function->positional_arguments,
            arguments->value.pair->first->value.symbol->identifier);

        arguments = arguments->value.pair->rest;
    }

    // okay we are done with positional arguments, lets check for
    // keywords,
    if (arguments->type != Ast_Node_Type_Pair) {
        if (arguments->type != Ast_Node_Type_Nil)
            create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
        return;
    }

    if (arguments->value.pair->first->type == Ast_Node_Type_Keyword &&
        string_equal(arguments->value.pair->first->value.keyword->identifier, "keys"))
    {
        arguments = arguments->value.pair->rest;
        if (arguments->type != Ast_Node_Type_Pair ||
            arguments->value.pair->first->type != Ast_Node_Type_Symbol)
        {
            create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
            return;
        }

        while (arguments->type == Ast_Node_Type_Pair) {
            if (arguments->value.pair->first->type == Ast_Node_Type_Keyword) {
                if (string_equal(arguments->value.pair->first->value.keyword->identifier, "rest"))
                    break;
                else {
                    create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
                    return;
                }
            }

            if (arguments->value.pair->first->type != Ast_Node_Type_Symbol) {
                create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
                return;
            }

            // we found a symbol (arguments->value.pair->first) for
            // the keyword args! Let's check if the next arguement is
            // :defaults-to
            Ast_Node* next = arguments->value.pair->rest;
            if (next->type == Ast_Node_Type_Pair &&
                next->value.pair->first->type == Ast_Node_Type_Keyword &&
                string_equal(next->value.pair->first->value.keyword->identifier,
                              "defaults-to"))
            {
                // check if there is a next argument too, otherwise it
                // would be an error
                next = next->value.pair->rest;
                if (next->type == Ast_Node_Type_Pair) {
                    append_to_keyword_argument_list(function->keyword_arguments,
                                                    arguments->value.pair->first->value.symbol->identifier,
                                                    next->value.pair->first);
                    arguments = next->value.pair->rest;
                } else {
                    create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
                    return;
                }
            } else {
                // No :defaults-to, so just add it to the list
                append_to_keyword_argument_list(function->keyword_arguments,
                                                arguments->value.pair->first->value.symbol->identifier,
                                                nullptr);
                arguments = next;
            }
        }
    }


    // Now we are also done with keyword arguments, lets check for
    // if there is a rest argument
    if (arguments->type != Ast_Node_Type_Pair) {
        if (arguments->type != Ast_Node_Type_Nil)
            create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
        return;
    }

    if (arguments->value.pair->first->type == Ast_Node_Type_Keyword &&
        string_equal(arguments->value.pair->first->value.keyword->identifier, "rest"))
    {
        arguments = arguments->value.pair->rest;
        if (arguments->type != Ast_Node_Type_Pair ||
            arguments->value.pair->first->type != Ast_Node_Type_Symbol)
        {
            create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
            return;
        }
        function->rest_argument = arguments->value.pair->first->value.symbol->identifier;
        if (arguments->value.pair->rest->type != Ast_Node_Type_Nil) {
            create_error(Error_Type_Ill_Formed_Lambda_List, arguments);
        }
    } else {
        printf("this should not happen?");
        create_error(Error_Type_Unknown_Error, arguments);
    }
}


int list_length(Ast_Node* node) {
    if (node->type == Ast_Node_Type_Nil)
        return 0;

    if (node->type != Ast_Node_Type_Pair) {
        create_error(Error_Type_Type_Missmatch, node);
        return 0;
    }

    int len = 0;
    while (node->type == Ast_Node_Type_Pair) {
        ++len;
        node = node->value.pair->rest;
        if (node->type == Ast_Node_Type_Nil)
            return len;
    }

    create_error(Error_Type_Ill_Formed_List, node);
    return 0;
}

bool is_truthy (Ast_Node* expression, Environment* env);

Ast_Node* extract_keyword_value(char* keyword, Parsed_Arguments* args) {
    // NOTE(Felix): This will be a hashmap lookup later
    for (int i = 0; i < args->keyword_keys->next_index; ++i) {
        if (string_equal(args->keyword_keys->data[i]->value.keyword->identifier, keyword))
            return args->keyword_values->data[i];
    }
    return nullptr;
}

Ast_Node* eval_arguments(Ast_Node* arguments, Environment* env, int *out_arguments_length) {
    *out_arguments_length = 0;
    if (arguments->type == Ast_Node_Type_Nil) {
        return arguments;
    }

    Ast_Node* evaluated_arguments = create_ast_node_pair(nullptr, nullptr);
    Ast_Node* evaluated_arguments_head = evaluated_arguments;
    Ast_Node* current_head = arguments;
    while (current_head->type == Ast_Node_Type_Pair) {
        try {
            evaluated_arguments_head->value.pair->first =
                eval_expr(current_head->value.pair->first, env);
        }
        current_head = current_head->value.pair->rest;

        if (current_head->type == Ast_Node_Type_Pair) {
            evaluated_arguments_head->value.pair->rest = create_ast_node_pair(nullptr, nullptr);
            evaluated_arguments_head = evaluated_arguments_head->value.pair->rest;
        } else if (current_head->type == Ast_Node_Type_Nil) {
            evaluated_arguments_head->value.pair->rest = current_head;
        } else {
            create_error(Error_Type_Ill_Formed_Arguments, arguments);
            return nullptr;
        }
        ++(*out_arguments_length);
    }
    return evaluated_arguments;
}

Ast_Node* eval_expr(Ast_Node* node, Environment* env) {
#define report_error(_type) {                   \
        create_error(_type, node);              \
        return nullptr;                         \
    }

    if (error)
        return nullptr;

    Ast_Node* ret = new(Ast_Node);
    switch (node->type) {
    case Ast_Node_Type_T:
    case Ast_Node_Type_Nil:
        return node;
    case Ast_Node_Type_Symbol: {
        Ast_Node* symbol;
        try {
            symbol = lookup_symbol(node->value.symbol, env);
        }
        return symbol;
    }
    case Ast_Node_Type_Number:
    case Ast_Node_Type_Keyword:
    case Ast_Node_Type_String:
        return node;
    case Ast_Node_Type_Pair: {
        Ast_Node* operator;
        if (node->value.pair->first->type != Ast_Node_Type_Built_In_Function &&
            node->value.pair->first->type != Ast_Node_Type_Function)
        {
            try {
                operator = eval_expr(node->value.pair->first, env);
            }
        } else {
                operator = node->value.pair->first;
        }

        Ast_Node* arguments = node->value.pair->rest;
        int arguments_length;

        // check for special form
        if (operator->type == Ast_Node_Type_Built_In_Function) {
            switch (operator->value.built_in_function->type) {
            case Built_In_Breakpoint: {
                print_environment(env);
#ifdef _DEBUG
                __debugbreak();
#endif
                return create_ast_node_nil();
            }
            case Built_In_Info: {
                try {
                    arguments_length = list_length(arguments);
                }
                if (arguments_length != 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }

                print(arguments->value.pair->first);

                Ast_Node* type = eval_expr(
                    create_ast_node_pair(
                        create_ast_node_symbol("type"),
                        create_ast_node_pair(arguments->value.pair->first, create_ast_node_nil())),
                    env);

                if (type) {
                    printf(" is of type ");
                    print(type);
                    printf("\n");
                    // just make sure type was not redefined and
                    // returns something that is not a keyword
                    if (type->type == Ast_Node_Type_Keyword &&
                        (string_equal(type->value.keyword->identifier, "dynamic-function") ||
                         string_equal(type->value.keyword->identifier, "dynamic-macro")))
                    {
                        Ast_Node* fun = eval_expr(arguments->value.pair->first, env);
                        printf("\nMacro? %s\n", (fun->value.function->is_macro) ? "yes" : "no");
                        if (fun->value.function->docstring)
                            printf("Docstring:\n==========\n%s\n\n", fun->value.function->docstring);
                        else
                            printf("No docstring avaliable\n");

                        printf("Arguments:\n==========\n");
                        printf("Postitional: {");
                        if (fun->value.function->positional_arguments->next_index != 0) {
                            printf("%s", fun->value.function->positional_arguments->identifiers[0]);
                            for (int i = 1; i < fun->value.function->positional_arguments->next_index; ++i) {
                                printf(", %s", fun->value.function->positional_arguments->identifiers[i]);
                            }
                        }
                        printf("}\n");
                        printf("Keyword:     {");
                        if (fun->value.function->keyword_arguments->next_index != 0) {
                            printf("%s", fun->value.function->keyword_arguments->identifiers[0]);
                            for (int i = 1; i < fun->value.function->keyword_arguments->next_index; ++i) {
                                printf(", %s", fun->value.function->keyword_arguments->identifiers[i]);
                            }
                        }
                        printf("}\n");
                        printf("Rest:        {");
                        if (fun->value.function->rest_argument)
                            printf("%s", fun->value.function->rest_argument);
                        printf("}\n");

                    }
                } else {
                    printf(" is not defined\n");
                    delete_error();
                }

                return create_ast_node_nil();
            }
            case Built_In_Macro:
            case Built_In_Lambda: {
                /*
                 *  (lambda ())
                 *  (lambda (x d) (+ 1 2) (- 1 2) (* 1 2))
                 */
                try {
                    arguments_length = list_length(arguments);
                }
                if (arguments_length == 0)
                    report_error(Error_Type_Wrong_Number_Of_Arguments);


                Function* function = new(Function);
                if (operator->value.built_in_function->type == Built_In_Macro) {
                    function->is_macro = true;
                } else {
                    function->is_macro = false;
                }

                // if parameters were specified
                if (arguments->value.pair->first->type != Ast_Node_Type_Nil) {
                    try {
                        assert_type(arguments->value.pair->first, Ast_Node_Type_Pair);
                    }
                    try {
                        parse_argument_list(arguments->value.pair->first, function);
                    }
                } else {
                    function->positional_arguments = create_positional_argument_list(1);
                    function->keyword_arguments = create_keyword_argument_list(1);
                    function->rest_argument = nullptr;
                }

                arguments = arguments->value.pair->rest;
                // if there is a docstring, use it
                if (arguments->value.pair->first->type == Ast_Node_Type_String) {
                    function->docstring = arguments->value.pair->first->value.string->value;
                    arguments = arguments->value.pair->rest;
                } else {
                    function->docstring = nullptr;
                }

                // we are now in the function body, just wrap it in an
                // implicit prog
                function->body = create_ast_node_pair(
                    create_ast_node_built_in_function("prog"),
                    arguments);

                Ast_Node* ret = new(Ast_Node);
                ret->type = Ast_Node_Type_Function;
                ret->value.function = function;
                return ret;
            }
            case Built_In_Let: {
                // (let ((a 10)(b 20)) (body1) (body2))
                try {
                    arguments_length = list_length(arguments);
                }
                if (arguments_length < 1)
                    report_error(Error_Type_Wrong_Number_Of_Arguments);

                Environment* let_env = create_child_environment(env, Environment_Type_Let);
                Ast_Node* bindings = arguments->value.pair->first;
                while (true) {
                    if (bindings->type == Ast_Node_Type_Nil) {
                        break;
                    } else if (bindings->type != Ast_Node_Type_Pair) {
                        report_error(Error_Type_Ill_Formed_Arguments);
                    }

                    Ast_Node* sym = bindings->value.pair->first->value.pair->first;
                    if(sym->type != Ast_Node_Type_Symbol) {
                        report_error(Error_Type_Ill_Formed_Arguments);
                    }
                    Ast_Node* rest_sym = bindings->value.pair->first->value.pair->rest;
                    if (rest_sym->type != Ast_Node_Type_Pair) {
                        report_error(Error_Type_Ill_Formed_Arguments);
                    }
                    if (rest_sym->value.pair->rest->type != Ast_Node_Type_Nil) {
                        report_error(Error_Type_Ill_Formed_Arguments);
                    }

                    Ast_Node* value = rest_sym->value.pair->first;

                    define_symbol(sym, value, let_env);

                    bindings = bindings->value.pair->rest;
                }

                arguments = arguments->value.pair->rest;

                Ast_Node* evaluated_arguments;
                try {
                    evaluated_arguments = eval_arguments(arguments, let_env, &arguments_length);
                }

                if (evaluated_arguments->type == Ast_Node_Type_Nil)
                    return evaluated_arguments;

                // skip to the last evaluated operand and return it,
                // we use eval_arguments here instead of doing it
                // manually, because we want to increase code reuse,
                // but at the cost that we have to find the end of the
                // list again
                while (evaluated_arguments->value.pair->rest->type == Ast_Node_Type_Pair) {
                    evaluated_arguments = evaluated_arguments->value.pair->rest;
                }
                return evaluated_arguments->value.pair->first;

            }
            case Built_In_And: {
                bool result = true;
                while (arguments->type != Ast_Node_Type_Nil) {
                    if (arguments->type != Ast_Node_Type_Pair) {
                        report_error(Error_Type_Ill_Formed_List);
                    }
                    try {
                        result &= is_truthy(arguments->value.pair->first, env);
                    }
                    arguments = arguments->value.pair->rest;

                    if (!result) return create_ast_node_nil();
                }

                return create_ast_node_t();
            }
            case Built_In_Or: {
                bool result = false;
                while (arguments->type != Ast_Node_Type_Nil) {
                    if (arguments->type != Ast_Node_Type_Pair) {
                        report_error(Error_Type_Ill_Formed_List);
                    }
                    try {
                        result |= is_truthy(arguments->value.pair->first, env);
                    }
                    arguments = arguments->value.pair->rest;

                    if (result) return create_ast_node_t();
                }

                return create_ast_node_nil();
            }
            case Built_In_Not: {
                try {
                    arguments_length = list_length(arguments);
                }
                if (arguments_length != 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }
                bool truthy;
                try {
                    truthy = is_truthy(arguments->value.pair->first, env);
                }
                if (truthy)
                    return create_ast_node_nil();
                return create_ast_node_t();
            }
            case Built_In_While: {
                try {
                    arguments_length = list_length(arguments);
                }

                if (arguments_length < 2) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }
                Ast_Node* condition = arguments->value.pair->first;
                Ast_Node* then_part = arguments->value.pair->rest;
                Ast_Node* result = create_ast_node_nil();
                while (eval_expr(condition, env)->type != Ast_Node_Type_Nil) {
                    result = eval_expr(then_part->value.pair->first, env);
                }
                return result;

            }
            case Built_In_If: {
                try {
                    arguments_length = list_length(arguments);
                }
                if (arguments_length != 2 && arguments_length != 3) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }

                Ast_Node* condition = arguments->value.pair->first;
                Ast_Node* then_part = arguments->value.pair->rest;
                Ast_Node* else_part = then_part->value.pair->rest;

                bool truthy;
                try {
                    truthy = is_truthy(condition, env);
                }
                Ast_Node* result;
                if (truthy)
                    try{
                        result = eval_expr(then_part->value.pair->first, env);
                    }
                else if (arguments_length == 3)
                    try {
                        result = eval_expr(else_part->value.pair->first, env);
                    }
                else return create_ast_node_nil();
                return result;
            }
            case Built_In_Quote: {
                arguments_length = list_length(arguments);
                if (arguments_length != 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }
                return arguments->value.pair->first;
            }
            case Built_In_Macro_Define:
            case Built_In_Define: {
                try {
                    arguments_length = list_length(arguments);
                }
                if (arguments_length != 2) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }

                Ast_Node* symbol = arguments->value.pair->first;

                if (symbol->type == Ast_Node_Type_Pair) {
                    try {
                        symbol = eval_expr(symbol, env);
                    }
                }

                if (symbol->type != Ast_Node_Type_Symbol) {
                    report_error(Error_Type_Type_Missmatch);
                }

                Ast_Node* value = arguments->value.pair->rest->value.pair->first;
                /* print(value); */
                try {
                    value = eval_expr(value, env);
                }
                /* print(value); */

                if (operator->value.built_in_function->type == Built_In_Macro_Define) {
                    /* printf("Defining %s in the macro env to be ", symbol->value.symbol->identifier); */
                    /* print(value); */

                    define_macro_symbol(symbol, value, env);
                }
                else
                    define_symbol(symbol, value, env);

                return value;
            }
            }

            // okay it is not a special form, so in any case we want
            // to evaluate the arguments; eval_arguments will also tell
            // us the arguments_length.
            Ast_Node* evaluated_arguments;
            try {
                evaluated_arguments = eval_arguments(arguments, env, &arguments_length);
            }

            switch (operator->value.built_in_function->type) {
            case Built_In_Addition: {
                return built_in_add(evaluated_arguments);
            }
            case Built_In_Subtraction: {
                return built_in_substract(evaluated_arguments);
            }
            case Built_In_Multiplication: {
                return built_in_multiply(evaluated_arguments);
            }
            case Built_In_Division: {
                return built_in_divide(evaluated_arguments);
            }
            case Built_In_Equal: {
                return built_in_equals(evaluated_arguments);
            }
            case Built_In_Greater: {
                return built_in_greater(evaluated_arguments);
            }
            case Built_In_Greater_Equal: {
                return built_in_greater_equal(evaluated_arguments);
            }
            case Built_In_Less: {
                return built_in_less(evaluated_arguments);
            }
            case Built_In_Less_Equal: {
                return built_in_less_equal(evaluated_arguments);
            }
            case Built_In_Mutate: {
                if (arguments_length != 2)
                    report_error(Error_Type_Wrong_Number_Of_Arguments);

                if (evaluated_arguments->value.pair->first->type == Ast_Node_Type_Nil ||
                    evaluated_arguments->value.pair->first->type == Ast_Node_Type_Keyword)
                {
                    report_error(Error_Type_Type_Missmatch);
                }

                Ast_Node* target = evaluated_arguments->value.pair->first;
                Ast_Node* source = evaluated_arguments->value.pair->rest->value.pair->first;

                *target = *source;
                return target;
            }
            case Built_In_Load: {
                if (arguments_length != 1)
                    report_error(Error_Type_Wrong_Number_Of_Arguments);

                if (evaluated_arguments->value.pair->first->type != Ast_Node_Type_String)
                    report_error(Error_Type_Type_Missmatch);

                Ast_Node* result;
                try {
                    result = built_in_load(
                        evaluated_arguments->value.pair->first->value.string->value, env);
                }
                return result;
            }
            case Built_In_Pair: {
                if (arguments_length != 2) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }
                return create_ast_node_pair(evaluated_arguments->value.pair->first, evaluated_arguments->value.pair->rest->value.pair->first);
            }
            case Built_In_First: {
                if (arguments_length != 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }
                if (evaluated_arguments->value.pair->first->type == Ast_Node_Type_Nil)
                    return create_ast_node_nil();
                if (evaluated_arguments->value.pair->first->type != Ast_Node_Type_Pair)
                    report_error(Error_Type_Type_Missmatch);

                return evaluated_arguments->value.pair->first->value.pair->first;
            }
            case Built_In_Rest: {
                if (arguments_length != 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }
                if (evaluated_arguments->value.pair->first->type == Ast_Node_Type_Nil)
                    return create_ast_node_nil();
                if (evaluated_arguments->value.pair->first->type != Ast_Node_Type_Pair)
                    report_error(Error_Type_Type_Missmatch);

                return evaluated_arguments->value.pair->first->value.pair->rest;
            }
            case Built_In_Eval: {
                if (arguments_length != 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }
                Ast_Node* result;
                try {
                    result = eval_expr(evaluated_arguments->value.pair->first, env);
                }
                return result;
            }
            case Built_In_Prog: {
                if (evaluated_arguments->type == Ast_Node_Type_Nil)
                    return evaluated_arguments;

                // skip to the last evaluated operand and return it,
                // we use eval_arguments here instead of doing it
                // manually, because we want to increase code reuse,
                // but at the cost that we have to find the end of the
                // list again
                while (evaluated_arguments->value.pair->rest->type == Ast_Node_Type_Pair) {
                    evaluated_arguments = evaluated_arguments->value.pair->rest;
                }
                return evaluated_arguments->value.pair->first;
            }
            case Built_In_List: {
                return evaluated_arguments;
            }
            case Built_In_Print: {
                if (arguments_length != 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }
                print(evaluated_arguments->value.pair->first);
                /* printf("\n"); */
                return arguments->value.pair->first;
            }
            case Built_In_Read: {
                if (arguments_length > 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }

                if (arguments_length == 1) {
                    Ast_Node* prompt = evaluated_arguments->value.pair->first;
                    if (prompt->type == Ast_Node_Type_String)
                        printf("%s", prompt->value.string->value);
                    else
                        print(evaluated_arguments->value.pair->first);
                }
                char* line = read_line();
                return create_ast_node_string(line, (int)strlen(line));
            }
            case Built_In_Type: {
                if (arguments_length != 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }

                Ast_Node_Type type = evaluated_arguments->value.pair->first->type;
                switch (type) {
                case Ast_Node_Type_Built_In_Function: return create_ast_node_keyword("built-in-function");
                case Ast_Node_Type_Function: {
                    if (evaluated_arguments->value.pair->first->value.function->is_macro)
                        return create_ast_node_keyword("dynamic-macro");
                    return create_ast_node_keyword("dynamic-function");
                }
                case Ast_Node_Type_Keyword:           return create_ast_node_keyword("keyword");
                case Ast_Node_Type_Nil:               return create_ast_node_keyword("nil");
                case Ast_Node_Type_T:                 return create_ast_node_keyword("t");
                case Ast_Node_Type_Number:            return create_ast_node_keyword("number");
                case Ast_Node_Type_Pair:              return create_ast_node_keyword("pair");
                case Ast_Node_Type_String:            return create_ast_node_keyword("string");
                case Ast_Node_Type_Symbol:            return create_ast_node_keyword("symbol");
                }
            }
            case Built_In_Exit: {
                if (arguments_length > 1) {
                    report_error(Error_Type_Wrong_Number_Of_Arguments);
                }

                if (arguments_length == 1) {
                    Ast_Node* error_code = evaluated_arguments->value.pair->first;
                    if (error_code->type != Ast_Node_Type_Number)
                        report_error(Error_Type_Type_Missmatch);

                    exit((int)error_code->value.number->value);
                }
                exit(0);
            }

            default:
                report_error(Error_Type_Not_Yet_Implemented);
            }

        }

        if (operator->type == Ast_Node_Type_Function) {
            if (!operator->value.function->is_macro) {
                try {
                    arguments = eval_arguments(arguments, env, &arguments_length);
                }
            }

            Ast_Node* result;
            try {
                result = apply_arguments_to_function(arguments, operator->value.function, env);
            }
            return result;
        }
    }
    default: {
#ifdef _DEBUG
        __debugbreak();
#endif
        report_error(Error_Type_Not_A_Function);
    }
    }
#undef report_error
}

bool is_truthy (Ast_Node* expression, Environment* env) {
    Ast_Node* result;
    try {
        result = eval_expr(expression, env);
    }
    if (result->type == Ast_Node_Type_Nil)
        return false;
    return true;

}