On 1/9/16 5:49 AM, Russel Winder via Digitalmars-d wrote:
On Thu, 2016-01-07 at 15:32 -0500, Andrei Alexandrescu via Digitalmars-
d wrote:
On 01/07/2016 02:02 PM, Russel Winder via Digitalmars-d wrote:
[…]
Got it, thanks. I took a look at a familiar topic - json grammars.
I just googled `boost spirit json` and followed through the top
result.
For C++, the grammar definition would be
https://github.com/cierelabs/json_spirit/blob/master/ciere/json/parse
r/grammar_def.hpp.
Then I googled `pegged json` and the top result led to
https://github.com/PhilippeSigaud/Pegged/blob/master/pegged/examples/
json.d.
Which do you like more?
Just a quick look I'm afraid, so very superficial at this stage:
The D code as presented is clearly simpler and easy to read. However
the D grammar is a string and not code so the anticipation is that
errors in the C++ code would be easier to find and correct. I guess the
question here is how good the compile time evaluation of strings is in
D and does it do good error reporting.
The string parser is custom code and issues errors as defined by the
library author. (I don't have experience with Pegged in particular.) I
think one difficulty with ETs is reporting line where errors occur in
multi-line strings. Language facilities could help here. This is an area
of strategic importance for D.
I do have extensive experience with error messages in C++ ETs, which
were and are inscrutable.
I still prefer the concept of Internal DSL explicitly in the code
rather than in strings just now, but this may still just be prejudice.
Prejudice can last only so long in the face of evidence.
Andrei
