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digitalmars.D.learn - Pure D frontend as library.

reply Alexandru Ermicioi <alexandru.ermicioi gmail.com> writes:
Hi team,

I'd like to ask a lazy question:
How easy is to use D compiler frontend without backend?

How complicated would be to write a transpiler, and from which 
files should you start modifications?

I'm wondering if something like 
https://typescripttolua.github.io/ could be done, but with d as 
language.

 From my limited knowledge, I should have an AST visitor that 
transpiles to target language, and some entry point for 
application which configures D frontend to use my AST visitor to 
generate code. I've no idea from where to start. If you know some 
documentation or tutorials, that would be appreciated.

Thanks,
Alexandru.
Dec 26 2022
next sibling parent reply "Richard (Rikki) Andrew Cattermole" <richard cattermole.co.nz> writes:
On 27/12/2022 8:13 AM, Alexandru Ermicioi wrote:

 How easy is to use D compiler frontend without backend?


Easy. 
https://github.com/dlang/dmd/blob/master/compiler/test/dub_package/frontend.d


 How complicated would be to write a transpiler, and from which files 
 should you start modifications?


That on the other hand... Yeah, things aren't great on that front. The 
thing you want to implement is what we call glue code and isn't really 
setup right now for this (nobody has tried like this, ignoring ldc/gdc 
as they modify it).
Dec 26 2022
parent reply Alexandru Ermicioi <alexandru.ermicioi gmail.com> writes:
On Monday, 26 December 2022 at 23:08:59 UTC, Richard (Rikki) 
Andrew Cattermole wrote:

...

 That on the other hand... Yeah, things aren't great on that 
 front. The thing you want to implement is what we call glue 
 code and isn't really setup right now for this (nobody has 
 tried like this, ignoring ldc/gdc as they modify it).


Hi, thx for information.

Any idea from which file should I start at least learning about 
this glue code?

Also, since this is not yet done, is there a way to insert this 
custom glue code without modifying D frontend source code?
If not which file should I register custom changes?

Thanks,
Alexandru.
Dec 27 2022
parent "Richard (Rikki) Andrew Cattermole" <richard cattermole.co.nz> writes:
On 27/12/2022 9:34 PM, Alexandru Ermicioi wrote:

 Any idea from which file should I start at least learning about this 
 glue code?


You can look at dmd's... but realistically the work hasn't been done at 
that level to make it easy to work with.

https://github.com/dlang/dmd/blob/master/compiler/src/dmd/glue.d

https://github.com/dlang/dmd/blob/master/compiler/src/dmd/gluelayer.d

Note how it doesn't let you use your own implementation. This is very 
much throwing you into the deep end without any help.
Dec 27 2022
prev sibling parent reply Johan <j j.nl> writes:
On Monday, 26 December 2022 at 19:13:01 UTC, Alexandru Ermicioi 
wrote:

 Hi team,

 I'd like to ask a lazy question:
 How easy is to use D compiler frontend without backend?

 How complicated would be to write a transpiler, and from which 
 files should you start modifications?

 I'm wondering if something like 
 https://typescripttolua.github.io/ could be done, but with d as 
 language.

 From my limited knowledge, I should have an AST visitor that 
 transpiles to target language, and some entry point for 
 application which configures D frontend to use my AST visitor 
 to generate code. I've no idea from where to start. If you know 
 some documentation or tutorials, that would be appreciated.


You can have a look at LDC's code, which does what you are saying.
LDC first initializes itself (`cppmain()`) and then calls 
`mars_mainBody` 
(https://github.com/ldc-developers/ldc/blob/e5c97c6468334c65130a654c8aec819c51dd6
d3/dmd/mars.d#L197) which reads source code files, does semantic analysis
(create AST; note that there is a ton of calls needed to complete SeMa), and
finally outputs object code.

I'd start by copying the initialization and SeMa parts and 
stopping before the codegen part, removing all things that you 
think you will not need.
The difficult thing is interpreting the AST. LDC does not use a 
visitor, don't get stuck on that idea, you don't necessarily need 
it. Documentation of the AST is not great; to discover what 
things mean / what needs to be done, consult the handling of AST 
nodes by LDC or DMD's glue layers.
Of course you don't have to implement everything at the start. 
Just get function definitions, function calls, and string 
definitions going first --> that's what your "hello world" needs 
;)

I have never looked at GDC's code, but I presume it is quite 
similar in this regard to LDC, so you can look at that too.

-Johan
Dec 27 2022
parent Stefan Koch <uplink.coder googlemail.com> writes:
On Tuesday, 27 December 2022 at 12:22:45 UTC, Johan wrote:
does semantic analysis (create AST; note that there is a ton of 
calls needed to complete SeMa), and finally outputs object code.

If you want to capitalize the word use SemA. ;)
Dec 27 2022