runtime evaluation

[hoya]

On Saturday, 14 December 2013 at 23:36:12 UTC, Marco Leise wrote:
> Am Sat, 14 Dec 2013 21:11:46 +0100
> schrieb "hoya" <sighoya at gmail.com>:
>
>> On Saturday, 14 December 2013 at 17:47:34 UTC, Marco Leise 
>> wrote:
>> > Am Sat, 14 Dec 2013 14:59:42 +0100
>> > schrieb "hoya" <sighoya at gmail.com>:
>> >
>> >> On Saturday, 14 December 2013 at 13:44:01 UTC, Marco Leise 
>> >> wrote:
>> >> 
>> >> > You can load libraries at runtime like OpenGL or a 
>> >> > database
>> >> > driver. This applies to all C and D libraries as well as 
>> >> > C++
>> >> > libraries to some extent.
>> >> >
>> >> Can you give me an example how to do this?
>> >
>> > Hmm, there are two options when it comes to dynamic linking.
>> >
>> > You can directly refer to the functions you use from some
>> > library. An example is std.net.curl in Phobos. You compile
>> > your program with "dmd -L-lcurl <source>" to link to the curl
>> > library which is written in C and common on Linux systems.
>> > This is the simple case where you don't need to write any
>> > extra code.
>> >
>> > If you want to load a plugin at runtime or OpenGL (which is a
>> > different library for each graphics card vendor) you will 
>> > need
>> > to use the dynamic linker (libdl.so) which handles this case:
>> > "dmd -L-ldl <source>" and then use "dlopen" and "dlsym" in
>> > your program to find the addresses of functions. Derelict 3 
>> > is
>> > a good example of loading libraries at runtime this way:
>> > https://github.com/aldacron/Derelict3
>> > It is a wrapper/binding collection for many multimedia/game
>> > related libraries and you can reuse its derelict.util module
>> > to load your own libraries at runtime.
>> >
>> > Which case are you interested in?
>> >
>> The Latter
>> > This can be done with dmd as
>> > well, but in both cases it is crutch to bring eval()-like
>> > functionality to a statically compiled language. :)
>> Hmm. An eval() method is good, if writing something like a 
>> Drepl. I've heard from someone that other people have tried 
>> some work on it.
>> Or good case, if you can use a dynamic mixin(). When read a 
>> string from input, then it is possible to create a structure 
>> like struct, class and so on. With dlopen() you need at least 
>> a library file, where all your code is written in, as I thin 
>> correctly. But with a dynamic mixin() you have the ability, to 
>> add structures in-memory. So this is more efficient.
>
> A simple REPL that doesn't remember any previous state is
> easily written today. It becomes difficult when you want to
> keep your state from command to command or try to delete
> previous definitions.
> For what you want there would have to be a JIT compiler in
> every D program in the first place. Interpreted languages and
> JIT compiled languages have an advantage here.
> eval() is more efficient in the way that you don't need to go
> though an external file and have the dynamic linker load it,
> yes. But even if a real eval() existed, there is no point in
> adding structs to the program that way, since the rest of the
> code isn't prepared to accept them. Sub-classes would work.
> I would look into using an interpreted or JIT compiled
> language from within D for the parts of your code that need
> to be dynamic. Take like LuaD for example:
> https://github.com/JakobOvrum/LuaD
> Python or JavaScript bindings would do as well.
I will keep this in mind, thanks.
Thanks all for helping!