Interpreting the D grammar

[MakersF via Digitalmars-d]

On Sunday, 2 August 2015 at 14:50:35 UTC, Jacob Carlborg wrote:
> I'm trying to read the D grammar [1] to enhance the D TextMate 
> bundle. If we take the add expression as an example. It's 
> defined like this in the grammar:
>
> AddExpression:
>     MulExpression
>     AddExpression + MulExpression
>     AddExpression - MulExpression
>     CatExpression
>
> And like this in the grammar made by Brian [2]:
>
> addExpression:
>       mulExpression
>     | addExpression ('+' | '-' | '~') mulExpression
>     ;
>
> I'm not so familiar with grammars but this looks like it's 
> recursive. Is it possible to translate this piece of grammar to 
> a regular expression? TextMate uses regular expressions and a 
> couple of enhancements/extensions to define a grammar for a 
> language.
>
> [1] http://dlang.org/grammar.html
> [2] https://rawgit.com/Hackerpilot/DGrammar/master/grammar.html

Of course it's recursive! Do you want the grammar to be able to 
only define a finite number of programs?

But in this case you could write the original grammar rule as
mul |
cat |
(mul|cat)((+|-) (mul|cat))* (+|-) (mul|cat)

but you lose the precedence of the operation as it is a flat list 
and not a tree