So, You Want To Write Your Own Programming Language?

[Don]

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.