Menu
Search

Forums

Forum Index

Jump to page: 1 2
Thread overview
No main() Error
Feb 04
monkyyy
Feb 12
monkyyy
February 02
Gravatar of Ron TarrantPosted by Ron TarrantReply
Ron Tarrant
Gravatar of Ron Tarrant


Reply

I'd like to suggest that an error condition be added wherein, if there is no main() function, the compiler will treat this as a fundamental error and report it upon exit.

Most of the code I write these days is in Python. I turned to D for a small project this morning and while doing some preliminary exploration into file handling, I got a "Declaration expected" error while trying to write a foreach() loop.

What it turned out to be is that I'd forgotten to wrap my code in a main() function. Dumb mistake, not the kind of mistake most would make. I'm too used to writing in Python, I guess.

I expect most people reading this will think this is so fundamental as to not be needed, but I'm hoping to avoid, in future, going around in circles for an hour and a half while trying to do something so trivial.

Thank you for your kind consideration of this matter.

February 02
Gravatar of Richard (Rikki) Andrew CattermolePosted by Richard (Rikki) Andrew Cattermole
in reply to Ron Tarrant		Reply
Richard (Rikki) Andrew Cattermole
Gravatar of Richard (Rikki) Andrew Cattermole
Posted in reply to Ron Tarrant


Reply
Due to separate compilation, the D compiler cannot know if a start address exists with a function provided for it.

The responsibility of this is the linker, which will error if no start address with executable code is provided.
February 04
Gravatar of Ron TarrantPosted by Ron Tarrant
in reply to Richard (Rikki) Andrew Cattermole		Reply
Ron Tarrant
Gravatar of Ron Tarrant
Posted in reply to Richard (Rikki) Andrew Cattermole


Reply

On Sunday, 2 February 2025 at 10:14:15 UTC, Richard (Rikki) Andrew Cattermole wrote:

>

Due to separate compilation, the D compiler cannot know if a start address exists with a function provided for it.

The responsibility of this is the linker, which will error if no start address with executable code is provided.

I guess I'm not being very clear. I'll try again...

On the first pass, I'd like to suggest that the compiler could check for an occurrence of "main" followed by "(" and spit out an error if it's not found.

Any of the following would avoid the error:

void main(

<returned type> main (

void main  (

And other variations thereof.

February 04
Gravatar of Richard (Rikki) Andrew CattermolePosted by Richard (Rikki) Andrew Cattermole
in reply to Ron Tarrant		Reply
Richard (Rikki) Andrew Cattermole
Gravatar of Richard (Rikki) Andrew Cattermole
Posted in reply to Ron Tarrant


Reply
On 04/02/2025 10:16 PM, Ron Tarrant wrote:
> On Sunday, 2 February 2025 at 10:14:15 UTC, Richard (Rikki) Andrew Cattermole wrote:
>> Due to separate compilation, the D compiler cannot know if a start address exists with a function provided for it.
>>
>> The responsibility of this is the linker, which will error if no start address with executable code is provided.
> 
> I guess I'm not being very clear. I'll try again...
> 
> On the first pass, I'd like to suggest that the compiler could check for an occurrence of "main" followed by "(" and spit out an error if it's not found.
> 
> Any of the following would avoid the error:
> 
> ```
> void main(
> 
> <returned type> main (
> 
> void main  (
> ```
> 
> And other variations thereof.

What do you mean by first pass?

The reasons for this to not work is because the compiler cannot do it, only the linker has the information needed to emit an error.

Syntax does not play a role in this.
February 04
Gravatar of Richard (Rikki) Andrew CattermolePosted by Richard (Rikki) Andrew Cattermole
in reply to Richard (Rikki) Andrew Cattermole		Reply
Richard (Rikki) Andrew Cattermole
Gravatar of Richard (Rikki) Andrew Cattermole
Posted in reply to Richard (Rikki) Andrew Cattermole


Reply
On 04/02/2025 10:20 PM, Richard (Rikki) Andrew Cattermole wrote:
> Syntax does not play a role in this.

I should clarify this, the compiler already has functions for checking if a function is a main function.

https://github.com/dlang/dmd/blob/89b93e8b0952e8bf5dd73020a23cd7cb1897adcb/compiler/src/dmd/func.d#L595

It looks like it can work without semantic analysis having been done too.
February 04
Gravatar of Ron TarrantPosted by Ron Tarrant
in reply to Richard (Rikki) Andrew Cattermole		Reply
Ron Tarrant
Gravatar of Ron Tarrant
Posted in reply to Richard (Rikki) Andrew Cattermole


Reply

On Tuesday, 4 February 2025 at 09:25:14 UTC, Richard (Rikki) Andrew Cattermole wrote:

>

On 04/02/2025 10:20 PM, Richard (Rikki) Andrew Cattermole wrote:

>

Syntax does not play a role in this.

I should clarify this, the compiler already has functions for checking if a function is a main function.

https://github.com/dlang/dmd/blob/89b93e8b0952e8bf5dd73020a23cd7cb1897adcb/compiler/src/dmd/func.d#L595

It looks like it can work without semantic analysis having been done too.

Thanks for the clarification.

I confess I know nothing about compiler/linker design.

Is it possible for the compiler, having read the code file, to pass along enough information to the linker so it knows that a) there is no main() function in the code file and b) the current build isn't a library, thus making it possible for the linker to inform the user in clearer language that something's off?

February 04
Gravatar of monkyyyPosted by monkyyy
in reply to Ron Tarrant		Reply
monkyyy
Gravatar of monkyyy
Posted in reply to Ron Tarrant


Reply

On Tuesday, 4 February 2025 at 19:41:09 UTC, Ron Tarrant wrote:

>

On Tuesday, 4 February 2025 at 09:25:14 UTC, Richard (Rikki) Andrew Cattermole wrote:

>

On 04/02/2025 10:20 PM, Richard (Rikki) Andrew Cattermole wrote:

>

Syntax does not play a role in this.

I should clarify this, the compiler already has functions for checking if a function is a main function.

https://github.com/dlang/dmd/blob/89b93e8b0952e8bf5dd73020a23cd7cb1897adcb/compiler/src/dmd/func.d#L595

It looks like it can work without semantic analysis having been done too.

Thanks for the clarification.

I confess I know nothing about compiler/linker design.

Is it possible for the compiler, having read the code file, to pass along enough information to the linker so it knows that a) there is no main() function in the code file and b) the current build isn't a library, thus making it possible for the linker to inform the user in clearer language that something's off?
changing the c abi isnt really on the table without replacing entire os's
youd be better off writing a "rdmd" clone that attempts to run the file if it gets the error places and top level statements in a main function
February 04
Gravatar of Paul BackusPosted by Paul Backus
in reply to Ron Tarrant		Reply
Paul Backus
Gravatar of Paul Backus
Posted in reply to Ron Tarrant


Reply

On Sunday, 2 February 2025 at 10:06:29 UTC, Ron Tarrant wrote:

>

Most of the code I write these days is in Python. I turned to D for a small project this morning and while doing some preliminary exploration into file handling, I got a "Declaration expected" error while trying to write a foreach() loop.

It sounds like what you are really asking for here is a better error message when the compiler encounters a statement outside of a function.

E.g., if the compiler sees a control-flow keyword like foreach or if at the top-level scope of a module, instead of saying "declaration expected", it could say something like "foreach statement is not allowed outside of a function."

I agree that this would be a worthwhile improvement.

February 05
Gravatar of Richard (Rikki) Andrew CattermolePosted by Richard (Rikki) Andrew Cattermole
in reply to Ron Tarrant		Reply
Richard (Rikki) Andrew Cattermole
Gravatar of Richard (Rikki) Andrew Cattermole
Posted in reply to Ron Tarrant


Reply
On 05/02/2025 8:41 AM, Ron Tarrant wrote:
> On Tuesday, 4 February 2025 at 09:25:14 UTC, Richard (Rikki) Andrew Cattermole wrote:
>> On 04/02/2025 10:20 PM, Richard (Rikki) Andrew Cattermole wrote:
>>> Syntax does not play a role in this.
>>
>> I should clarify this, the compiler already has functions for checking if a function is a main function.
>>
>> https://github.com/dlang/dmd/ blob/89b93e8b0952e8bf5dd73020a23cd7cb1897adcb/compiler/src/dmd/ func.d#L595
>>
>> It looks like it can work without semantic analysis having been done too.
> 
> Thanks for the clarification.
> 
> I confess I know nothing about compiler/linker design.
> 
> Is it possible for the compiler, having read the code file, to pass along enough information to the linker so it knows that a) there is no `main()` function in the code file and b) the current build isn't a library, thus making it possible for the linker to inform the user in clearer language that something's off?

The compiler doesn't need to do anything extra.

All linkers can and will error if the start address / main function is missing.

What you are asking for is a nice customized error message for D.

Which as far as I'm aware is not supported by any linker.
February 05
Gravatar of Ron TarrantPosted by Ron Tarrant
in reply to Paul Backus		Reply
Ron Tarrant
Gravatar of Ron Tarrant
Posted in reply to Paul Backus


Reply

On Tuesday, 4 February 2025 at 22:14:40 UTC, Paul Backus wrote:

>

It sounds like what you are really asking for here is a better error message when the compiler encounters a statement outside of a function.

E.g., if the compiler sees a control-flow keyword like foreach or if at the top-level scope of a module, instead of saying "declaration expected", it could say something like "foreach statement is not allowed outside of a function."

I agree that this would be a worthwhile improvement.

Yes, well put. And thanks for the support.

« First   ‹ Prev
1 2
Next ›   Last »