Ast_Node* built_in_add(Ast_Node* operands) {
    double sum = 0;
    while (operands->type == Ast_Node_Type_Cons_Cell) {
        assert_type(operands->value.cons_cell->first, Ast_Node_Type_Number);
        sum += operands->value.cons_cell->first->value.number->value;
        operands = operands->value.cons_cell->rest;
    }

    return create_ast_node_number(sum);
}

Ast_Node* built_in_substract(Ast_Node* operands) {
    assert_type(operands->value.cons_cell->first, Ast_Node_Type_Number);
    double difference = operands->value.cons_cell->first->value.number->value;

    operands = operands->value.cons_cell->rest;
    while (operands->type == Ast_Node_Type_Cons_Cell) {
        assert_type(operands->value.cons_cell->first, Ast_Node_Type_Number);

        difference -= operands->value.cons_cell->first->value.number->value;
        operands = operands->value.cons_cell->rest;
    }
    return create_ast_node_number(difference);
}

Ast_Node* built_in_multiply(Ast_Node* operands) {
    assert_type(operands->value.cons_cell->first, Ast_Node_Type_Number);
    double product = operands->value.cons_cell->first->value.number->value;

    operands = operands->value.cons_cell->rest;
    while (operands->type == Ast_Node_Type_Cons_Cell) {
        assert_type(operands->value.cons_cell->first, Ast_Node_Type_Number);

        product *= operands->value.cons_cell->first->value.number->value;
        operands = operands->value.cons_cell->rest;
    }
    return create_ast_node_number(product);
}

Ast_Node* built_in_divide(Ast_Node* operands) {
    assert_type(operands->value.cons_cell->first, Ast_Node_Type_Number);
    double quotient = operands->value.cons_cell->first->value.number->value;

    operands = operands->value.cons_cell->rest;
    while (operands->type == Ast_Node_Type_Cons_Cell) {
        assert_type(operands->value.cons_cell->first, Ast_Node_Type_Number);

        quotient /= operands->value.cons_cell->first->value.number->value;
        operands = operands->value.cons_cell->rest;
    }
    return create_ast_node_number(quotient);
}