Using DMD 2.0.69.2, the following code:

extern (C) double sqrt(double x);
enum q = sqrt(4.0);

gives the error:

Error: sqrt cannot be interpreted at compile time, because it has no available source code

But if I do:

import std.math;
enum q = sqrt(4.0);

There is no problem. So two questions:

1) Why exactly can't the compiler call a C function at compile time whereas it can call a D function?

2) <same as above> ... which itself only in the end calls that very same C function IIANM?

I see druntime/import/core/math.d l 91:

double sqrt(double x);  /* intrinsic */

-- 
Shriramana Sharma, Penguin #395953

On 01/01/16 12:52 AM, Shriramana Sharma wrote:
> Using DMD 2.0.69.2, the following code:
>
> extern (C) double sqrt(double x);
> enum q = sqrt(4.0);
>
> gives the error:
>
> Error: sqrt cannot be interpreted at compile time, because it has no
> available source code
>
> But if I do:
>
> import std.math;
> enum q = sqrt(4.0);
>
> There is no problem. So two questions:
>
> 1) Why exactly can't the compiler call a C function at compile time whereas
> it can call a D function?
>
> 2) <same as above> ... which itself only in the end calls that very same C
> function IIANM?
>
> I see druntime/import/core/math.d l 91:
>
> double sqrt(double x);  /* intrinsic */

From what I've been able to tell, std.math have some special yucky rules about it and intrinsics.
It will make it very hard to split std.math up.

Rikki Cattermole wrote:

> It will make it very hard to split std.math up.

I have no desire to split std.math up. :-)

What I desire to do is be able to call a C library from a D template like octal to compute a string at compile time.

Is this possible or not?

-- 
Shriramana Sharma, Penguin #395953

On 01/01/16 1:05 AM, Shriramana Sharma wrote:
> Rikki Cattermole wrote:
>
>> It will make it very hard to split std.math up.
>
> I have no desire to split std.math up. :-)

I do though.

> What I desire to do is be able to call a C library from a D template like
> octal to compute a string at compile time.
>
> Is this possible or not?

No, source is not available.

Shriramana Sharma wrote:

> What I desire to do is be able to call a C library from a D template like octal to compute a string at compile time.

To be more explicit, I wrote a library in C since it's much leaner size-wise than the D code (although admittedly much *much* more tedious to write especially with all those string manipulations) and since it's callable from other languages like Python too.

None of those other languages have CTFE AFAICS. I would like to provide at least the D wrapper to the C library with a template which will enable CTFE computation via the library (it's just a string to string conversion). But the D compiler is complaining that it cannot call the C function at compile time even though the library is installed under /usr/local/lib and Python is able to access it via CTypes.

Please help!

-- 
Shriramana Sharma, Penguin #395953

Rikki Cattermole wrote:

>> Is this possible or not?
> 
> No, source is not available.

Why, is it because the D compiler is already linked to the C library (and hence knows where the functions are located and such), but not to my library? I mean, I even gave -L-lmylib and all that, but of course now I realize that that is only telling the *linker* about the lib. How do I tell the compiler to the lib? If Python CTypes can query and find out any library with the SO filename I throw at it, can't a D compiler?

-- 
Shriramana Sharma, Penguin #395953

On 01/01/16 1:11 AM, Shriramana Sharma wrote:
> Shriramana Sharma wrote:
>
>> What I desire to do is be able to call a C library from a D template like
>> octal to compute a string at compile time.
>
> To be more explicit, I wrote a library in C since it's much leaner size-wise
> than the D code (although admittedly much *much* more tedious to write
> especially with all those string manipulations) and since it's callable from
> other languages like Python too.
>
> None of those other languages have CTFE AFAICS. I would like to provide at
> least the D wrapper to the C library with a template which will enable CTFE
> computation via the library (it's just a string to string conversion). But
> the D compiler is complaining that it cannot call the C function at compile
> time even though the library is installed under /usr/local/lib and Python is
> able to access it via CTypes.
>
> Please help!

As I said its just not possible.
Either port it to D and extern(C) it so it is accesible from other languages or not have CTFE support.

On 01/01/16 1:14 AM, Shriramana Sharma wrote:
> Rikki Cattermole wrote:
>
>>> Is this possible or not?
>>
>> No, source is not available.
>
> Why, is it because the D compiler is already linked to the C library (and
> hence knows where the functions are located and such), but not to my
> library? I mean, I even gave -L-lmylib and all that, but of course now I
> realize that that is only telling the *linker* about the lib. How do I tell
> the compiler to the lib? If Python CTypes can query and find out any library
> with the SO filename I throw at it, can't a D compiler?

You misunderstand, its hardcoded into the CTFE evaluator. That is what an intrinsic is.

Rikki Cattermole wrote:

> You misunderstand, its hardcoded into the CTFE evaluator. That is what an intrinsic is.

What do you mean hardcoded into the CTFE evaluator? Surely you aren't suggesting that the D compiler contains its own implementation of the functions already implemented in libc?

-- 
Shriramana Sharma, Penguin #395953

On 01/01/16 1:29 AM, Shriramana Sharma wrote:
> Rikki Cattermole wrote:
>
>> You misunderstand, its hardcoded into the CTFE evaluator. That is what
>> an intrinsic is.
>
> What do you mean hardcoded into the CTFE evaluator? Surely you aren't
> suggesting that the D compiler contains its own implementation of the
> functions already implemented in libc?

Yes and no.
It has a small subset of functions which it consider intrinsics.
Intrinsics are only a way to tell the compiler hey go call x and give me the result.

Remember, if you don't have the source you can't execute it.
Unless you provide an escape hatch which is what intrinsics are.