[std.database] at compile time

[Don]

On 16.10.2011 17:39, Ary Manzana wrote:
> On 10/16/11 4:56 AM, foobar wrote:
>> Don Wrote:
>>
>>> On 16.10.2011 04:16, Ary Manzana wrote:
>>>> On 10/15/11 5:00 PM, Marco Leise wrote:
>>>>> Am 15.10.2011, 18:24 Uhr, schrieb Ary Manzana<ary at esperanto.org.ar>:
>>>>>
>>>>>> On 10/14/11 5:16 PM, Graham Fawcett wrote:
>>>>>>> On Fri, 14 Oct 2011 21:10:29 +0200, Jacob Carlborg wrote:
>>>>>>>
>>>>>>>> On 2011-10-14 15:26, Andrei Alexandrescu wrote:
>>>>>>>>> On 10/14/11 6:08 AM, Jacob Carlborg wrote:
>>>>>>>>>> On 2011-10-14 12:19, foobar wrote:
>>>>>>>>>>> Has anyone looked at Nemerle's design for this? They have an SQL
>>>>>>>>>>> macro which allows to write SQL such as:
>>>>>>>>>>>
>>>>>>>>>>> var employName = "FooBar"
>>>>>>>>>>> SQL (DBconn, "select * from employees where name =
>>>>>>>>>>> $employName");
>>>>>>>>>>>
>>>>>>>>>>> what that supposed to do is bind the variable(s) and it also
>>>>>>>>>>> validates the sql query with the database. This is all done at
>>>>>>>>>>> compile-time.
>>>>>>>>>>>
>>>>>>>>>>> My understanding is that D's compile-time features are powerful
>>>>>>>>>>> enough to implement this.
>>>>>>>>>>
>>>>>>>>>> You cannot connect to a database in D at compile time. You could
>>>>>>>>>> some
>>>>>>>>>> form of validation and escape the query without connecting to the
>>>>>>>>>> database.
>>>>>>>>>
>>>>>>>>> A little SQL interpreter can be written that figures out e.g. the
>>>>>>>>> names
>>>>>>>>> of the columns involved.
>>>>>>>>>
>>>>>>>>> Andrei
>>>>>>>>
>>>>>>>> But you still won't be able to verify the columns to the actual
>>>>>>>> database
>>>>>>>> scheme?
>>>>>>>
>>>>>>> One approach would be to write a separate tool that connects to the
>>>>>>> database and writes out a representation of the schema to a source
>>>>>>> file. At compile time, the representation is statically imported,
>>>>>>> and
>>>>>>> used to verify the data model.
>>>>>>>
>>>>>>> If we had preprocessor support, the tool could be run as such,
>>>>>>> checking the model just before passing the source to the compiler.
>>>>>>
>>>>>> Yeah, but you need a separate tool.
>>>>>>
>>>>>> In Nemerle it seems you can do everything just in Nemerle...
>>>>>>
>>>>>> It would be awesome if CTFE would be implemented by JITting
>>>>>> functions,
>>>>>> not by reinventing the wheel and implementing a handcrafted
>>>>>> interpreter...
>>>>>
>>>>> I wonder if that would work well with cross-compiling. If you blindly
>>>>> JIT functions, they may end up using structs of the wrong size, or
>>>>> integers with different endianness. Compile for 64-bit on a 32-bit
>>>>> machine. What size is size_t during CTFE?
>>>>
>>>> I don't understand this quite well. I want JITted functions to just
>>>> generate code that ultimately will be compiled. It's like what CTFE is
>>>> doing now, except that instead of doing it by interpreting every bit
>>>> and
>>>> spec of the language you would compile the function, run it to generate
>>>> code, and then compile the code for the target machine.
>>> [snip]
>>>> Maybe I'm not taking something into account... what is it?
>>>
>>> You're assuming that the compiler can run the code it's generating. This
>>> isn't true in general. Suppose you're on x86, compiling for ARM. You
>>> can't run the ARM code from the compiler.
>>>
>>
>> This is quite possible in Nemerle's model of compilation.
>> This is the same concept as XLST - a macro is a high level transform
>> from D code to D code.
>>
>> 1. compile the macro ahead of time into a loadable compiler
>> module/plugin.
>> the plugin is compiled for the HOST machine (x86) either by a separate
>> compiler
>> or by a cross-compiler that can also compile to its HOST target.

YES!!! This is the whole point. That model requires TWO backends. One 
for the host, one for the target.
That is, it requires an entire backend PURELY FOR CTFE.

Yes, of course it is POSSIBLE, but it is an incredible burden to place 
on a compiler vendor.