So, You Want To Write Your Own Programming Language?

[Andrei Alexandrescu]

On 1/22/14 4:53 AM, Don wrote:
> On Wednesday, 22 January 2014 at 04:29:05 UTC, Walter Bright wrote:
>> http://www.reddit.com/r/programming/comments/1vtm2l/so_you_want_to_write_your_own_language_dr_dobbs/
>>
>
> Great article. I was surprised that you mentioned lowering positively,
> though.
>
> I think from DMD we have enough experience to say that although lowering
> sounds good, it's generally a bad idea. It gives you a mostly-working
> prototype very quickly, but you pay a heavy price for it. It destroys
> valuable semantic information. You end up with poor quality error
> messages, and counter-intuitively, you can end up with _more_ special
> cases (eg, lowering ref-foreach in DMD means ref local variables can
> spread everywhere). And it reduces possibilities for the optimizer.
>
> In DMD, lowering has caused *major* problems with AAs, foreach. and
> builtin-functions, and some of the transformations that the inliner
> makes. It's also caused problems with postincrement and exponentation.
> Probably there are other examples.
>
> It seems to me that what does make sense is to perform lowering as the
> final step before passing the code to the backend. If you do it too
> early, you're shooting yourself in the foot.

There's a lot of value in defining a larger complex language in terms of 
a much simpler core. This technique has been applied successfully by a 
variety of languages (Java and Haskell come to mind).

For us, I opine that the scope statement would've had a million subtle 
issues if it weren't defined in terms of try/catch/finally.

My understanding is that your concern is related to the stage at which 
lowering is performed, which I'd agree with.


Andrei