On a low level, I want something like this code to work:
    string[] arr;      // this can be any suitable type

    arr ~= "a";        // data is compile-time constant

    enum f = arr[0];   // fails with "Error: variable arr cannot be read at compile time"
    enum b = arr[$-1]; // fails with "Error: variable arr cannot be read at compile time"

More generic description: I'm looking for a way to have a container (or any other type) that I can manipulate during compile time. Operations needed are similar to stack functionality: get first/last element, push_back and pop_back.

How can I do that?

On Monday, 31 August 2020 at 20:39:10 UTC, Andrey Zherikov wrote:
> How can I do that?

You can use a normal string[] BUT it is only allowed to be modified inside its own function.

Then you assign that function to an enum or whatever.


string[] ctGenerate() {
   string[] list;
   list ~= "stuff";
   return list;
}

enum list = ctGenerate();


That's all allowed. But CTFE is now allowed to read or modify anything outside its own function; you can't have two separate function calls build up a shared list (unless you can somehow call them both together like `enum list = ctGenerate() ~ other_thing();`

On Mon, Aug 31, 2020 at 08:39:10PM +0000, Andrey Zherikov via Digitalmars-d-learn wrote:
> On a low level, I want something like this code to work:
>     string[] arr;      // this can be any suitable type
> 
>     arr ~= "a";        // data is compile-time constant
> 
>     enum f = arr[0];   // fails with "Error: variable arr cannot be read at
> compile time"
>     enum b = arr[$-1]; // fails with "Error: variable arr cannot be read at
> compile time"
> 
> More generic description: I'm looking for a way to have a container (or any other type) that I can manipulate during compile time. Operations needed are similar to stack functionality: get first/last element, push_back and pop_back.
> 
> How can I do that?

First, read this article:

	https://wiki.dlang.org/User:Quickfur/Compile-time_vs._compile-time

Secondly, to answer your question: write regular ("runtime") code for manipulating your data (also regular "runtime" data), and simply run the function during CTFE. Almost 90% of the language is usable during CTFE, so that's all you really need.


T

-- 
Маленькие детки - маленькие бедки.

On Monday, 31 August 2020 at 20:44:16 UTC, Adam D. Ruppe wrote:
> On Monday, 31 August 2020 at 20:39:10 UTC, Andrey Zherikov wrote:
>> How can I do that?
>
> You can use a normal string[] BUT it is only allowed to be modified inside its own function.
>
> Then you assign that function to an enum or whatever.
>
>
> string[] ctGenerate() {
>    string[] list;
>    list ~= "stuff";
>    return list;
> }
>
> enum list = ctGenerate();
>
>
> That's all allowed. But CTFE is now allowed to read or modify anything outside its own function; you can't have two separate function calls build up a shared list (unless you can somehow call them both together like `enum list = ctGenerate() ~ other_thing();`


The thing I'm trying to implement is: I have a function foo(string s)() and some "state"; this function should override this "state" (using "s" param) for all code within this function (note that code can execute other modules that can refer to the same "state"). The problem is that I need this overridden "state" to be compile-time constant to be used in mixin. Any ideas how I can do this?

On 9/1/20 2:19 PM, Andrey Zherikov wrote:
> On Monday, 31 August 2020 at 20:44:16 UTC, Adam D. Ruppe wrote:
>> On Monday, 31 August 2020 at 20:39:10 UTC, Andrey Zherikov wrote:
>>> How can I do that?
>>
>> You can use a normal string[] BUT it is only allowed to be modified inside its own function.
>>
>> Then you assign that function to an enum or whatever.
>>
>>
>> string[] ctGenerate() {
>>    string[] list;
>>    list ~= "stuff";
>>    return list;
>> }
>>
>> enum list = ctGenerate();
>>
>>
>> That's all allowed. But CTFE is now allowed to read or modify anything outside its own function; you can't have two separate function calls build up a shared list (unless you can somehow call them both together like `enum list = ctGenerate() ~ other_thing();`
> 
> 
> The thing I'm trying to implement is: I have a function foo(string s)() and some "state"; this function should override this "state" (using "s" param) for all code within this function (note that code can execute other modules that can refer to the same "state"). The problem is that I need this overridden "state" to be compile-time constant to be used in mixin. Any ideas how I can do this?

string overrideState(string s)
{
   // work your magic here, it's normal D code!
}

void foo(string s)()
{
   mixin(overrideState(s));
}

-Steve

On Tuesday, 1 September 2020 at 18:19:55 UTC, Andrey Zherikov wrote:
> The thing I'm trying to implement is: I have a function foo(string s)() and some "state"; this function should override this "state" (using "s" param) for all code within this function (note that code can execute other modules that can refer to the same "state"). The problem is that I need this overridden "state" to be compile-time constant to be used in mixin. Any ideas how I can do this?

In regular code it should look like this:

private string[] state;

string getCurrentState()
{
  return state[$-1];
}

void foo(string s)
{
  state ~= s;
  scope(exit) state = state[0..$-1];

  ...
}

On Tuesday, 1 September 2020 at 18:57:30 UTC, Steven Schveighoffer wrote:
> string overrideState(string s)
> {
>    // work your magic here, it's normal D code!
> }
>
> void foo(string s)()
> {
>    mixin(overrideState(s));
> }

Unfortunately this won't work if there is a function 'bar' in different module that calls 'foo':

void bar()
{
   foo!"bar";
}

void foo(string s)()
{
  mixin(overrideState(s));

  ...
  mixin("bar()");     // just for illustration
}

On 9/1/20 3:09 PM, Andrey Zherikov wrote:
> Unfortunately this won't work if there is a function 'bar' in different module that calls 'foo':

You should post a full example you expect to work or not work, then we can discuss.

I think it should work (I've tried it), but there are several problems that could possibly happen with your code, and it's hard to tell what you mean by "won't work" with the incomplete code that you posted.

-Steve

On Tuesday, 1 September 2020 at 19:38:29 UTC, Steven Schveighoffer wrote:
> On 9/1/20 3:09 PM, Andrey Zherikov wrote:
>> Unfortunately this won't work if there is a function 'bar' in different module that calls 'foo':
>
> You should post a full example you expect to work or not work, then we can discuss.
>
> I think it should work (I've tried it), but there are several problems that could possibly happen with your code, and it's hard to tell what you mean by "won't work" with the incomplete code that you posted.
>
> -Steve

Sorry for confusion. I'm trying to implement compile-time scripting and the idea is pretty simple: I have a script file and I want to convert it to D code during compilation. I've done some things but stuck at the point when script includes another script.

For simplicity, let's say that script file has commands (one per line) with syntax "<command><space><parameter>" and only two commands available= "msg" to print text and "include" to include another script.
Here is my code:
==============
void parseFile(string file)()
{
    enum script = import(file);
    mixin(parseScript(script));
}
string parseScript(string script)
{
    string code;

    foreach(line; script.lineSplitter())
    {
        auto idx = line.indexOf(' ');

        switch(line[0..idx])
        {
            case "msg"=
                code ~= "writeln(\"" ~ line[idx+1..$] ~ "\");";
                break;
            case "include"=
                code ~= "parseFile!\"" ~ line[idx+1..$] ~ "\";";
                break;
            default= break;
        }
    }
    return code;
}
void main()
{
    parseFile!"script";
}
==============
Everything works well until I have included scripts in subdirectories:
├── dir1
│   ├── dir2
│   │   └── script
│   └── script
└── script
Content:
============== script
msg hello
include dir1/script
============== dir1/script
msg hello from dir1
include dir2/script
============== dir1/dir2/script
msg hello from dir1/dir2
==============

Compilation fails with "Error: file `"dir2/script"` cannot be found or not in a path specified with `-J`" (I used simple dmd -J. -run parser.d) which is expected because parse* functions do not track the directory where the script is located.

In this simple example the issue can be fixed by passing path to script as a parameter to parseScript function. But this doesn't seem to be flexible and extendable solution because there can be other commands that might call parseFile indirectly (they can even be in other modules).

Theoretically this can be solved by doing something like this but it doesn't work because "static variable `paths` cannot be read at compile time":
==============
string[] paths;
void parseFile(string file)()
{
    enum path = paths.length > 0 ? buildPath(paths[$-1], file.dirName()) : file.dirName();

    paths ~= path;
    scope(exit) paths = paths[0..$-1];

    enum script = import(buildPath(path, file));
    mixin(parseScript(script));
}
==============
Note that the whole point is to do this parsing at compile time.

On 9/2/20 5:56 AM, Andrey Zherikov wrote:

> ==============
> Everything works well until I have included scripts in subdirectories:
> ├── dir1
> │   ├── dir2
> │   │   └── script
> │   └── script
> └── script
> Content:
> ============== script
> msg hello
> include dir1/script
> ============== dir1/script
> msg hello from dir1
> include dir2/script
> ============== dir1/dir2/script
> msg hello from dir1/dir2
> ==============
> 
> Compilation fails with "Error: file `"dir2/script"` cannot be found or not in a path specified with `-J`" (I used simple dmd -J. -run parser.d) which is expected because parse* functions do not track the directory where the script is located.
> 
> In this simple example the issue can be fixed by passing path to script as a parameter to parseScript function. But this doesn't seem to be flexible and extendable solution because there can be other commands that might call parseFile indirectly (they can even be in other modules).
> 
> Theoretically this can be solved by doing something like this but it doesn't work because "static variable `paths` cannot be read at compile time":
> ==============
> string[] paths;
> void parseFile(string file)()
> {
>      enum path = paths.length > 0 ? buildPath(paths[$-1], file.dirName()) : file.dirName();
> 
>      paths ~= path;
>      scope(exit) paths = paths[0..$-1];
> 
>      enum script = import(buildPath(path, file));
>      mixin(parseScript(script));
> }
> ==============
> Note that the whole point is to do this parsing at compile time.


OK, NOW I see where your code is coming from. The issue is that you need the directory of the script imported to be the "local directory". Your solution will not work -- you can't mixin code that is not available at compile time.

Here is what I would do instead:

string parseScript(string filename, string script)
{
    string code;
    string base = dirName(filename);
    if(base[$-1] != '/') base ~= '/';
    foreach(line; script.lineSplitter())
    {
        auto idx = line.indexOf(' ');

        switch(line[0..idx])
        {
            case "msg":
                code ~= "writeln(\"" ~ line[idx+1..$] ~ "\");";
                break;
            case "include":
            {
                code ~= `parseFile!"`;
                string importfile = line[idx+1 .. $];
                if(!importfile.startsWith('/')) // relative path
                     code ~= base;
                code ~= importfile ~ `";`;
                break;
            }
            default: break;
        }
    }
    return code;
}

And pass the filename to this function in addition to the script source.

-Steve