• Eduard Staniloiu (28/28) Jan 15 2019 Hello, everyone!
• H. S. Teoh (68/88) Jan 16 2019 Great!

Eduard Staniloiu <edi33416 gmail.com> writes:

Hello, everyone!

I'm posting this as a followup to the positive feedback that 
Andrei's Bison related post( 
https://forum.dlang.org/thread/1c3d8e77-ce4c-6310-0afd-e6518728299f erdani.org)
has received.

Akim Demaille has started "turning the wheels" towards adding a D 
backend to GNU Bison.

There currently is a skeleton for D on the Bison master 
(https://savannah.gnu.org/git/?group=bison) that you can use to 
check out the backend. A good starting point to explore this 
feature is to go into the .../share/doc/bison/examples/d 
directory and to run "make" there.

There is no documentation and Akim doesn't have experience with 
the D programming language, that is where we, the D community, 
can lend a helping hand.
I'm posting this to ask for your help in getting the D backend 
feature into Bison.

There is work needed to bring this skeleton up to speed and into 
an official release: writing tests and documentation, 
refactoring, etc.
Akim is going to provide assistance with the process, but he is 
not to be expected to carry this task on his own.

A good first step is to have a look at examples/d/calc.y and see 
if it can be improved.
 From there we should start improving the skeleton, fixing 
mistakes and writing documentation on the way.

I sincerely hope this opportunity will catch your interest.

Cheers,
Edi

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Tue, Jan 15, 2019 at 03:13:44PM +0000, Eduard Staniloiu via Digitalmars-d
wrote:
[...]
 I'm posting this as a followup to the positive feedback that Andrei's
 Bison related post(
 https://forum.dlang.org/thread/1c3d8e77-ce4c-6310-0afd-e6518728299f erdani.org)
 has received.
 
 Akim Demaille has started "turning the wheels" towards adding a D
 backend to GNU Bison.

Great!


 There currently is a skeleton for D on the Bison master
 (https://savannah.gnu.org/git/?group=bison) that you can use to check
 out the backend. A good starting point to explore this feature is to
 go into the .../share/doc/bison/examples/d directory and to run "make"
 there.
 
 There is no documentation and Akim doesn't have experience with the D
 programming language, that is where we, the D community, can lend a
 helping hand.
 I'm posting this to ask for your help in getting the D backend feature
 into Bison.

I glanced briefly at the various D-related notes, and took a good look
at the generated calc.d in the examples/d directory.  Here are some
comments:

- I understand that the current D codegen is mainly based on the
  existing Java backend, so unsurprisingly quite a few places shows
  signs of being very Java-like rather than D-like.  Hopefully, with
  some work, we can get it to emit more idiomatic D. :-)

- The first question I have is how much the Bison API depends on the
  lexer being swappable at runtime, i.e., via the Lexer interface.  I'm
  having a hard time imagining that there will be many use cases where
  you'd like to swap lexers with the same parser at runtime, so I'm
  thinking the parser should simply take the lexer type as a template
  argument, with sig constraints ensuring that whatever type the user
  passes in implements the necessary methods for the parser to work.
  This lets us bind the lexer to the parser at compile-time, and elide
  the vtable indirection (it can still be done if the user passes in a
  class).

- Along a similar vein, I'm wondering if the generated parser ought to
  be a class at all, or is the inheritability of the parser a key Bison
  feature?  Also, are language-specific directives supported /
  encouraged?  If so, it might be worthwhile to let the user choose
  whether to use a struct/template API vs. an OO class-based API.

- On a more high-level note, I'm wondering how flexible the API of the
  parser can be.  The main thought behind this is that given enough
  flexibility, we may be able to target, e.g.,  nogc,  safe, pure, etc..
  With  safe probably a pretty important target, if it's possible to do
  so.  While this depends of course on the exact code the user puts into
  the .y file, a worthy goal is to make the emitted D code  safe (pure,
  etc.) by default unless the user writes non- safe code in the .y file.

- How flexible can the lexer API be?  For example, currently
  lexer.yyerror takes a string argument, which requires using std.format
  in various places.  If permissible, I'd like to have yyerror take a
  generic input range instead, so that we can avoid the inherent memory
  allocation of std.format (e.g., if we wish to target  nogc).
  
- Also, is it possible to use exceptions instead of yyerror()?  Or would
  that deviate too far from Bison's design?

- On a more general note, I'd like to make the parser/lexer APIs
  range-based as much as possible, esp. when it comes to
  string-handling.  But I'm just not sure how much the APIs are expected
  to conform to the analogous C/C++/Java APIs.

- I wonder if YYSemanticType could use std.variant somehow instead of a
  raw union, which would probably force the parser to be  system.

- Can Bison handle UTF-8 lexer/parser rules?  D uses UTF-8 by default,
  and it would be nice to leverage this support instead of manually
  iterating over bytes, as is done in a few places.

- Some minor points that should be easy to fix:

   - The YYACCEPT, YYABORT, etc., symbols really should be declared as
     enums rather than static ints.

   - D does support the #line directive.  So these should be emitted as
     they are in C/C++. (I noticed they currently only appear as
     comments.)

   - YYStack needs to be fixed to avoid the reallocate-on-every-push
     problem on arrays. A common beginner's mistake.  Also, if we're
     going to target  nogc (not 100% sure about that right now), we may
     have to forego built-in arrays altogether.


[...]
 Akim is going to provide assistance with the process, but he is not to
 be expected to carry this task on his own.

[...]

Dumb question: If I wanted to contribute some commits, do I have to sign
up on savannah.gnu.org?  What's the procedure for submitting pull
requests?  (Sorry, I glanced over the README's and the FAQ at
savannah.gnu.org but didn't find a clear answer.)


T

-- 
May you live all the days of your life. -- Jonathan Swift